Cork Souterrain Engineering. A Tale of Masons and Tunnellers
The purpose of this chapter is to look at the construction aspects of souterrains. It is a way of thinking about what, in a technical sense, souterrain builders knew, thought and achieved; as evidenced across the wide range of sites which have been discovered in South Munster over the past 250 years or so.
Engineering is a step by step decisions making and problem solving of technicalities process. Engineering the built rural landscape in early medieval Ireland.Who are the most skilled? Were they the ringfort builders, the caher and cashel builders, the drystone wall builders, builders in timber being replicated in stone. Were the monasteries the main source of much of this knowledge; the most skilled architects, engineers, quarrymen and stone cutters, artisans and labourers? Were they the ones most capable of organising major or lesser construction projects? How integral to every aspect of early medieval societal life were they? Was there a gradation of investment and quality of site construction according to the status of an intended occupant? Were some souterrains simply the crude efforts of hermitage monks with limited skills, manpower and resources?
Stating the Requirement
Who was the site to be built for and by who would it be built? Was it to be an anchorhold for one of several anchorites wishing solitude within the periphery of a monastic demesne? Was it to be a cellar and/or anchorhold attached to a church or oratory? Was it a place to protect those seeking sanctuary or valuable religious artefacts such as church plate? Was it to be the place of retreat (reclusorium) and retirement of a Christian community leader e.g. an early bishop? Was it to be part of a hermitage or a small ‘cell group’ where only two or three gathered in Christ’s name? Was it to be the place of a pardoner and confessor where the dirt of sins (sallach) was removed, a place of aural confession in the Gaelic fashion for converts prior to Easter Sunday and for ? Was it to be a place of poor hermits or wealthy abbots? Would the poor hermits build it for themselves to occupy or would the monks of the monastery build it for their abbots? Was it to be a cellar for the monastery cellarer? Such initial decisions would most likely impact on the standard of construction which resulted at the site. One is tempted to look beneath the lines of the 6th century Rule of St. Benedict for indicators of how souterrains forms, be they cells or cellars, would have been contextualised by the daily workings of an early monastery influenced by his Rule; a rule influential throughout Western Christendom in its day – and more so subsequently.
Caves versus Artificial Caves
As pointed out by Lucas (1971-73, 170) natural caves are ‘virtually confined to the limestone districts’ of Ireland. While there are masonry built souterrains in limestone areas of Cork e.g. Fermoy, the relative absence of souterrains in other limesetone places of Cork such as East Cork may be the result of suitable natural caves. Might this explain an apparent lack of souterrains in the hinterland of the great monastery of Cloyne (Cluain Uamha i.e. the cluain monastery of the caves)? A dependent hermitage, perhaps of the 7th century, and associated with Cloyne was once situated at Rostellan, in Cork Harbour nearby. Between Rostellan creek (now a lake) and Farsid (a fording place) – where a spittal once was, lies the townland of Hermitage with Kilteskin (Cill Teach Sescín, the cell of the house of six heads or of the marshland) townland beside it. In the 19th century the Rostellan demesne was notable for its limestone caves. Did monks at Rostellan once use such caves? Is it a hermit in prayer (male or female) which is carved on a slab beside the holy well of Kilteskin, the crucifixion carved on its other side?
However, I do not think that this is an adequate explanation for a very small show of souterrain discoveries in South East Cork compared with central and west Cork. I am more of the view that clay tunnelled sites in Muskerry and Carbery are the result of a deliberate choice, trend or familiarity with traditions in lands elsewhere; where tunnelling as a modus operandi for creating underground spaces was the norm. In other words, they represent an expansion to Irish shores of established practice elsewhere, and are therefore not an indigenous development.
The corpus of masonry constructed sites on record displays a variety of forms. Some examples appear to reflect room forms, dimensions, and room alignments comparable with tunnelled sites. Attempts at representing barrel vaulted ceilings- some successful, others not so depending on the strengths of the glacial till, as found in some tunnelled sites, do not occur in masonry constructed sites. For reasons of economy, some masonry sites such as Coolgarrif in County Cork (investigated by Cork speleologist J.C.Coleman, 1945, 112-114), a domed beehive cell connected to two linked passageways, show evidence of a combination of methods where one of the passageways has walls cut in the glacial till, but not masonry lined, except for their upper reaches. Similar common sense approaches are evident in tunnelled sites were insufficient glacial till is available in certain spots at the chosen site, the solution being to cut in to the underlying rock mantle in order to give sufficient height to a room for its required need.
In other cases tunnelled sites have drystone built entrance shafts, as for example where a short entrance length with a steep gradient is the engineering solution chosen, rather than a longer one with a gentler gradient. Information of this nature helps to open up an understanding of the problems encountered by souterrain builders and the engineering solutions they brought to bear on such problems. Their understanding of the geology of the sites chosen for both masonry and tunnelled souterrains, was considerable, as much in relation to masonry construction as to tunnelling techniques. To what extent this knowledge was monastic in origin or secular, is a good question.
The value of using test pits at a chosen site, as a preliminary to understanding how to approach creating a particular souterrain, is something which requires further study. At tunnelled sites vertical pits would allow observation of the underlying geology i.e. the depth of glacial till at several points in the site area, the quality, density and strength of the till to hold room forms. How much rock tunnelling below the soil substrate would be required. Once these shafts were created, and potential problems assessed, horizontal tunnelling could be undertaken from the bottom of the shaft either in one, two or more directions with spoil removal perhaps by bag. What might have happened afterwards to the clay and soil removed is anyone’s guess.
Regarding masonry sites, a variety of forms exist in the Cork archaeological record. They vary from beehive domed cells, to passageways, narrow galleries, rectangular rooms to suit functional objectives in the design of an individual souterrain. The stone quarried for such building work can vary from limestone to sandstone to slate; though limestone chippings for either coursed or rubble wall construction appears to be most common depending on local geology and carriage distance from a quarry source. Regarding rock tunnelled sites, very few are on record and what are known are mostly in the Muskerry and Carbery parts of the Kingdom of Desmond i.e. largely in the same regions as clay tunnelled sites. Some of the characteristics of rock tunnelled sites can differ from clay tunnelled ones. As to how many exist, it is not possible to estimate as they are less likely ot collapse due to surface activity and are often only discovered as a result of chance encounters e.g. Dunisky was discovered by a boy in the 1930s hunting rabbits with a ferret. Rock tunnelled sites in Cork have been discovered also at Currahaly, Knockdrum monastic enclosure, Brackcloon.
To what extent clay tunnelled and rock tunnelled sites are distinct from one another if a all, regardless of surface contexts, is a matter for further research. To what extent the forms of masonry constructed sites are reflective of surface context is also a matter for further research. The masonry constructed souterrains can range in overall size from ……to …….
In design form they they can range from a domed beehive shaped room with a passageway leading to it, to a group of two or three domed beehive cells, to two long galleries set at right angles to each other and joined by a creepway, to stretches of passageways aligned at angles to each other without creepways, to rectangular rooms either aligned or parallel or a combination of both, and other forms.
Wooden Structures as Souterrains: Liscreagh and Ballycatteen
Another point of interest is that the discovery of evidence for wooden posts, to indicate perhaps a wooden superstructure, at one of the Ballycatteen souterrains (Souterrain C). Liscreagh, in Muskerry, Co. Cork had a subterranean structure d in a uni-vallate ringfort discovered during turf cutting. It was described as being 5 feet of solid log over a passage built of timber. In cross section the passage was 3 ft square and boarded all around with black bog oak.
Given that this site was discovered in the course of turf cutting it is interesting to query a relationship between turf constructed huts and the use of timber panelling for their interior walls; not uncommon in a nordic vernacular architecture tradition.
Raheennamaddra in County Limerick may reflect the adaptation, at some period in time, of some souterrains, initially built as cellars, to function as lodgings by removing the capstones and replacing them with a gabled (thatched?) roof structure. But, without evidence to support it, this idea is nothing more than speculation. Posthole evidence at some of the Cush, County Limerick small conjoined ringforts souterrains made also indicate perhaps wattle and daub structures above ground. In County Fermanagh in Ulster at Coolcran evidence for timber walling in a souterrain was found (Williams 1985).
A group of timber walled souterrains dating to the 3rd century BC is reported from Dalladies in Kincardinshire, in north east Scotland (Henderson 2007, 145). Also in Scotland, a souterrain at Auchrannie, Brodick, on the Isle of Arran is reported as using timber wall lining (https://doi.org/10.3366/saj.2017.0077). The dating for the site spreads from the last centuries BC to circa 200 AD with the souterrain not being infilled until early medieval times – if I correctly interpret the online report.
Were evidence for corn husks, walnut shells or oat husks to be found collapsed into a souterrain it would be interesting to consider insulation techniques (Evans 2013, 41-42).
Engineering Solutions and the creation of Souterrains Architectures
Architecturally, as examples of vernacular architecture in the rural landscape, souterrains present many different shapes and forms. Furthermore they are created using either of two engineering methods and sometimes a combination of both: one method used to create souterrains is that of tunnelling into glacial substrata or rock; the other method is the ‘cut and cover’ approach where a trench is excavated to a certain depth and width, within which a dry masonry structure composed of walls – consisting of courses of stone chippings, often with slight corbelling near the top – is constructed. The standard of the masonry work is noticeable in that frequently, the wall interiors are ‘plumb’ and ‘flush’ suggesting the use of either truncated A frames or some method of wooden shuttering as part of the construction process to create a smooth interior wall surface. The use of the corbelling technique for beehive chambers and in some passageways, has interesting parallels with the knowledge of dry masonry skills evident in County Kerry; at Gallarus oratory, Reask early monastic site, and at the major settlement site at Fahan, all close to the western end of the Dingle peninsula, as well as at Leacanabuile (Land area of ….)and Cahergal (Bright Caher) on the Iveragh peninsula and at Skellig Michael.
This category of souterrain structure is then roofed with flat stone slabs and finally the trench is closed off and concealed by backfilling using the original soil from the trench. Some sparse evidence exists that on some occasions wood may have been used in the construction of walls and roofs.
If one were to take the view that some tig faoi talaimh (meaning house underground) souterrains were used as habitation sites during the period of Celtic Christianity – both by secular as well as ecclesiastical persons – and that subsequently later generations of persons at certain social class levels within the secular population occupied them long term, then were descriptive names applied to such persons?As advised to the Munster antiquarian Charles Smith in the 1740s AD souterrains were places of the ‘Farbologes, a people of whom there is much mention in their [native Gaelic] MSS which name signifies no more than a creeping man, or one who lived in a cave’ (Smith 1774 edition, Vol. 2, 408). Smith also had the terms [advised by native scholars?] Terrignenae meaning ‘born from the earth’ and Antricolae – so named because of ‘their living in caves’.
How different were rock as distinct from clay tunnelled, as distinct from dry stone built, were chamber environments? Underground space offers a more stable environment temperature compared with the surface landscape. However, underground environments can be wet, damp and cold places. Damp, wet conditions result from water seepage, percolation from the surface. Was there an engineering solution to this e.g. a drystone built, thatched and/or sod built structure covering the surface above the souterrain? To provide heat was body heat sufficient i.e. the human body is equivalent to a 100 watt light bulb? Because the souterrain is an underground space there is greater heat retention than on the surface. A build up of such heat over a few hours would be lost at a slower rate than on the surface. Would this also lead to a drier environment underground? Would the provision of a surface ‘porch’ structure such as a clochán or a timber cubicle with a make-shift door covering the opening of the souterrain entrance shaft? Was the latter evidenced by some examples of post holes found above the entrances to the Cush, County Limerick, souterrains or a folklife reference to doors connected with caves at Burren townland near Courtmacsherry, County Cork or an example of doors to cellars in a hill slope in a place somewhere beyond Rosscarbery?
How frequently was some form of lighting used e.g. taper, rush light, tallow candle, oil lamp or small fire? How frequent or infrequent were fire boxes and vents above them acting as flues used? How stuffy and airless were such environments especially when occupied? Were such conditions suitable for cellar environments storing root crops or wine or dried meat products? Was some type of venting necessary in such circumstances? Was air circulation achieved solely by means of vents placed in the masonry infill of construction shafts or as small shafts i.e. ’spike holes’ drilled through clay or rock ceilings to the surface where they may or may not be capped with a small stone slab? How many were required e.g. one per chamber as at Fassagh in Cork? What is to be learnt from the curvature of the vent from the handbell chamber at Oldcourt, Cork or from the very long ‘trench with trough’ running from Chamber 5 at Curraghcrowley, Cork? Do they indicate a desire to distance or obscure the location of the souterrain from where a vent exits or where smoke from a chimney box flue might exit? Was a ‘through passage’ with chambers opening off it a means of funnelling airflow from the souterrain entrance, if kept open, thereby removing the need for individual chamber vents? Was the number of occupants at any one time a factor in deciding if any or how many vents were made either in ceilings or in construction shaft masonry work?
How damp and wet might the floors of chambers get? If used as lodgings were rushes or straw used as flooring and bedding? If food was consumed in such environments what evidence might survive? Remnants of nuts? The bones of small animals or bones from certain parts of larger animals? How might the environments within souterrains have performed and changed from the Medieval Warm Period circa 900 to 1300 AD and then during the Medieval Mini Ice Age circa 1300 to 1850 AD? There are sufficient research questions in relation to souterrain interior environments to justify a specific field study in its own right.
Where to situate the souterrain
There are several questions which might be asked about this. Was the intended souterrain to be situated within or in proximity to existing surface structures? Surface monuments which enclose souterrains include earthen ringforts and stone built cahers. Were souterrains built into existing surface enclosures, or were enclosures built to enclose souterrains i.e. were ringfort ramparts built to enclose souterrains and were caher walls built to enclose them? What was the maximum number of souterrain ever built in a single ringfort? Were long souterrain passages folded (zigzagged) in order to limit the amount of ringfort space to be undermined by subterranean structures? Were ringfort banks and ditches built with the intention of incorporating souterrain spaces? If so, would that explain why masonry built cahers have wall chambers? Was what was done in an earthen enclosure the same as that done in a masonry built enclosure?
Furthermore, was the idea of using such enclosures absorbed by early monasticism from existing vernacular, secular, traditions? When a ringfort or caher became the place of the subterranean cell (cave) of a preacher, saint, local church founder or hermit did an oratory come to be built on the surface; later to be the place of a parish church? Were the first burials placed in the vicinity of the cell, enclosed later by a graveyard wall or boundary delimiter, to evolve in to parish graveyards if that site became a parish church and if not then a cilleen burial place? Further research on this might provide more in-depth explanations for the folk tradition of cilleen burials. Do explanations of this nature explain the presence of ogham stones and souterrains in church burial grounds and in cilleens? If the souterrain was to be built/ tunnelled in a place where no surface structures existed did some such sites evolve into church sites while others did not? If so why not? Were some hermitages (early monasteries – bearing in mind that the original meaning of a monastery was the cell of a single monk) enclosed while others were not?
The practice of ‘enclosure’, of defining/delimiting a sacred space, was a well understood concept in early Christianity especially perhaps when the sacred area was in close proximity to other surface monuments or structures as in a community setting, religious or secular. Within the caher or rath (rampart or termon) the lios space it encloses can be very large e.g. a lios mór to enclose the precincts and immediate peripheral land of a large monastic settlement or it can be a 20 metre diameter ringfort interior. The site may reference itself as a lios mór emphasising the enclosure or as a cill mór emphasising the monastic cells there.
Within the lios space of enclosures, big or small, souterrains are found beneath and entered from circular as well as rectangular surface structures. Where such rectangular structures originally oratories and were the circular structures cell chambers? Were the circular structures the same as clocháns either in enclosures or not? Were some situated at terraced places either in sloping ground or along cliff faces? Were some thatch roofed and semi-subterranean; a mid-way structure between the beehive dome souterrain and a clochán? Was Souterrain C at Ballycatteen a variation on this theme? At sites like Leacanabuile, County Kerry were the interior rectangular structures already in place before the souterrain or do they represent subsequent building activity due to an increased population and its activities?
Were some clocháns built as surface doorways to souterrain entrances and if so were there equivalent structures in wood or wattle and daub? Were masonry entrance structures i.e. box/porch structures, incorporating ogham stones, an alternative to a clochán or wooden structure? There are many questions which still need investigation in the field.
Tunnelled sites, Depth beneath the ground and ceiling stability
As a result of trial pits, a decision can be made as to what depth the chambers can be placed at beneath the ground surface. Also, a decision can be made in regard to what height a chamber can be i.e. can a sufficient height be achieved for a person to occupy the space without creating a weak ceiling, unstable and too close to the surface. It was observed at some sites that surface activity e.g. mechanical equipment, tractors, had caused a flaking away of soil from some ceilings leaving a floor deposit. This would not have happened in Medieval times one presumes. If the depth of suitable subsoil i.e. suitable to retain the void required for the chamber to remain structurally stable as a clay-cut void, was insufficient what other options were available? These options appear to have been either to cut the floor of the chamber a little deeper and into the surface of the rock underneath or alternatively introduce a masonry element into part of the site’s construction.
Subsoils and Souterrain Builders
If local knowledge indicated that a clay tunnelled site was not feasible was a decision made to create a rock tunnelled site as at Curraghcrowley, Brackcloon and Dunisky, all in County Cork? Or, were other factors involved in making the decision? What factors influenced the choice of a rock tunnelled structure rather than a masonry constructed one? Were they to do with the nature of the bedrock and the technicalities of tunnelling? Were similar considerations made regarding clay tunnelled sites? Were masonry constructed souterrains an alternative solution, and preferable, to tunnelled sites? Could more be achieved architecturally by means of masonry construction? Or, are the reasons for such choices more cultural and social, tradition and function oriented, rather than having anything to do with skills and materials available? Was the choice indicative of chronological phases, the tunnelled souterrain being a predecessor of the masonry forms?
Soils, Subsoils, Glacial Till, Engineering and South Munster
The peninsulas of Dingle, Iveragh, Beara, Sheep’s Head and the Mizen are largely mountainous land areas where peaty podzols and blanket peat predominate. Along the shores of each of them pockets of brown podzols are to be found. From Bantry Bay mountainous terrain spreads north eastwards towards Killarney and beyond across the mountain ranges of the Shehy and Derrynasaggart and Mullockareirk Mountains with westward projections across the Boggeraghs and Nagles, to the Knockmaeldowns, the Monavullagh and Comeragh Mountains brown podzolics, gleys and acid brown earths are to be found also on the ridges and lower lying mountain ranges, In association with the brown podzolics glacial till is to be found connected with both limestone and sandstone areas of bedrock, limestone till being more gravel like in nature compared with more clayey tills associated with sandstone and mudstone areas.
The brown podzolics and acid brown earths are good soils for agriculture with an implication that they are areas more attractive to higher densities of population once cleared of natural vegetation cover. As places into which to tunnel clay-cut souterrains they appear to have a suitable depth and spread of subsoil suitable for the creation of such sites and the structural stability of such sites below the ground surface. Peaty soils spreading across the higher mountain ranges of the South West peninsulas and their foothills lack glacial till and so are not suitable for them except perhaps in random pockets where till may occur.
The alternative to clay tunnelling is therefore either to excavate in rock or use masonry in whatever suitable depth of soil is available. Another alternative is to construct on the surface of the land using sod cover to insulate masonry structures. By such means an underground tradition of clochán building can become a subterranean one where suitable depths of subsoil are available. In either case the option of rock tunnelling can be avoided. Where subsoils are more gravel rather than clay based, as it seems in limestone areas, a desire to retain the subterranean nature of a clochán tradition for whatever cultural reasons, such as concealment and solitude, can be accomplished by means of dry masonry construction in a trench: the ‘cut and cover’ method of site construction.
Furthermore, in similar fashion other architectural forms of souterrains can be replicated from tunnelled examples to masonry examples and vice versa; However, whereas a ‘barrel-vault- imitation in the shaping of a clay or rock tunnelled cubicle in a souterrain can be accomplished in these media, the dome, using the technique of corbelling is the only alternative or a ‘flat roof’ is the only alternative for masonry consturction to expand a ‘passage’ construction into a chamber but with limitations of structural feasibility.
Examples of the use of ‘flat roofs’ using masonry construction have been recorded at such sites as Roovesmore and Knockshanawee both in Aglish Parish, Co. Cork and another example from Waterford is Drumlohan. In all three cases Ogham stones were used in the roof construction; but only Drumlonan ses drystone walls whereas the Cork sites had clay walls, something also notable at the Ballynock North souterrain site which had 15 Ogham stones and was located in a ringfort. One wonders if it is the nature of rock type, soils and glacial till in South Leinster which dictates the lack of souterrains there or are the reasons more to do with cultural issues and influences from abroad?
Why does the spread of clay tunnelled souterrains in Cork appear to die out at the north side of the Blackwater River; something also notable for the spread of Ogham stones with which clay-cut souterrains are also associated e.g. Underhill, County Cork?
Therefore to conclude, is there a basis for seeing the cluster and ribbon densities of clay-tunnelled souterrains, practically unique to South Munster, as something which is a consequence of sticking to deeper spreads of more clayey glacial tills indicating agricultural settlements (secular and monastic) in the soil pockets of brown podzolics along the peninsular coastlines of the south west? Was it the case in the limestone areas of South Munster that even though there was sufficient subsoil for a tunnelled souterrain the subsoil was not structurally stable enough leading to the use of masonry construction? Was it the case that when, due to a lack of suitable subsoil, and concerns about the density of the bedrock and its ‘workability’ for available tunnelling skills and suitability for such, that the only remaining option was surface construction?
A certain depth of subsoil is necessary, regardless of its quality, for use of the dry masonry approach to souterrain construction, something which also impacts on the practicalities of internal space dimensions for passage and cubicle widths and heights as dictated by the precise widths and depths of the subsoil deposit at the souterrain’s location. In the case of rock tunnelled sites the upper levels of bedrock types which have a ‘slatey cleavage’ may be easily workable to a certain degree, the denser rock levels beneath requiring greater effort, skills, tools and time to tunnel It is evident in some clay tunnelled sites that the subsoil deposit spread beneath the site was variable in depth and directional extent as a consequence of which at some clay tunnelled sites portions of walls and floors were chiselled 30 to 60 cms into the surface of the bedrock to allow for a little more chamber (cubicle) height. Dunisky however, which I interpret as a site influenced by non-native i.e. Norman construction, has some of its chambers (cubicles) tunnelled into deeper, denser rock levels; the blade marks of the picks or ‘coal chisels’ used are still evident in abundance in the ceilings.
In South Munster Brown Podzolics are mainly concentrated, and for the chief soil type, from the eastern side of Bantry Bay north to Ballyvourney to Mallow and then follow a line eastwards south of the Blackwater River to Dungarvan Bay. North of this is a limestone belt where acid Brown Earths are dominant.
In the Brown Podzolics south of the Blackwater River and apart from the ‘Brown Podzolics and Gleys’ of the hill and mountain ranges there are belts of Acid Brown Earths in a belt which runs the Bride River (western) to Youghal Bay with further pockets in the Carrigaline and Ballycotton localities. In Dingle and Iveragh Peninsulas and spreading into West Cork are the Peaty Podzolics of this mountainous area. There are coastal pockets along each peninsula from Dingle to Mizen Head of Brown Podzolics and a further stretch of these extends from Killorglin to Killarney. The Brown Podzolics and the Acid Brown Earths are agriculturally fertile soils; The Acid Brown Earths sit on a mixed sandstone and limestone glacial till. The Brown Podzolics sit on a sandstone and shale till. Consequently, the area of land south of the Blackwater to the sea coast, south of it, is largely composed of this type of glacial till and it is in this land area that the majority of known clay-tunnelled souterrains are found, as well as in the coastal pockets where it is located. the glacial till type underlying the Acid Brown Earths appears to have been less favoured for this type of site possibly for structural engineering reasons.
The peaty Podzols which dominate the peninsular areas (Dingle to Mizen) lie on rock and perhaps this dictated the absence of clay-tunnelled sites in favour of rock tunnelled or ‘cut and cover’ method drystone built souterrains; alternatively, it may have provided the rational for surface level replicas concealed beneath sod coverings or uncovered; It is worth asking if the clochaun ‘beehive dome’ shape is a translation to surface level of the souterrain beehive domes of the Clondulane (Fermoy) region; Both, very effectively, use the art of drystone corbelling and the distribution of clocháns, as currently understood, is largely a phenomenon of the western coastline of Ireland. Is the existence of such surface structures largely the result of factors to do with subsoil types?
Engineering and the Bedrock of South Munster
The bedrock in South Munster is largely sandstone with belts of limestone cover in the river valleys of the Bandon, Lee and Blackwater rivers. There is also a limestone belt which runs from beyond Tralee Bay southwards to Coolmaine Harbour and then eastwards to the Lakes of Killarney. On the north eastern side of Bantry Bay another area of limestone occurs spreading northwards to the Pass of Keimineigh. Two further belts of limestone spread from Dunmanus Bay and Roaringwater Bay eastwards spreading south towards Kinsale and towards Myrtleville on the west side of Cork Harbour, there are also some banks of limestone in the areas of Clonakilty Bay and Courtmacasherry Bay. The band which links Dunmanus Bay to the Kinsale area underlies the Bandon River while portions of another band carry the River Lee. The west to east section of the River Blackwater overlies a limestone band while lands north of the Mallow to Fermoy stretch of the river are on the edge of a limestone plain stretching from Charleville to Buttevant to Mitchelstown to Clonmel, an area known as the Golden Vale. The mountain ranges in South Munster are largely of sandstones, mudstones and slate. Beyond Dungarvan eastwards the rock is basalt, ryolite and slate.
The Technicalities of Building
Tunnelled site Construction Process
Perhaps the driving factor behind the creation of the souterrain was an answer to two questions i.e. who was the site for and how frequently was it to be used to be used?
Once answered the process of construction cold begin and perhaps one might interpret this activity as having three phases i.e. initial, main and completion.
Tunnelled souterrains and engineering method
From a materials perspective there are two types of tunnelled souterrains i.e. clay cut sites and rock cut sites. There is an abundance of the former, a dearth of the latter and perhaps this is due to the fact that collapse, the usual circumstances of discovery, is less common in rock cut sites than it is with clay cut ones, particularly due to agricultural surface on the surface. With rock cut sites it is more to do with chance discovery e.g. a ferret at Dunisky, a farmer digging a hole at Curraghhaly, an archaeological dig at Knockdrum (Farrandau). For Munster there is a significant number clay-cut sites on record an example being Kilcondy, County Cork. while the number of rock cut site is very few. It is important to distinguish between rock or clay or masonry elements being used in a souterrain versus those souterrains which are totally or predominately rock-cut i.e. there is an evident intention by the person creating the site to carry out the work as a rock or clay tunnelled site, rather than it being a case of adapting the methods to suit the spread and depth of clay available at a particular site. This need to determine whether a single method was to be used or a combination of methods was determined by using test pits which when successful would then become the means of tunnelling and extraction of spoil (the construction pits) until eventually closed in with some masonry courses and an upper fill of soil.
The Raw Materials
The ‘green field scenario’ for a tunnelled souterrain in clay was as follows: A decision to create a souterrain is made based on need and requirement. Requirement is derived from practise elsewhere and an exemplar specific or rough is in the mind of the tunneller and associates. The surface activity at the site which dictates the need may be secular or ecclesiastical, it may be a clearing in a forest, it may be a mountain’s upper reaches. Tree cover in a forest may have roots which do not descend to the level of a souterrain’s ceiling, they may go no further than the humus layer. The skill level of the tunneller will determine the amount of forethought, planning and preparation. If the intention is to create the souterrain as a clay cut site , then the first order of business is to determine if the area of the surface beneath which the souterrain is to be tunnelled has sufficient spread and depth of suitable subsoil to sustain tunnelled space without collapsing. So, the method of doing this is to excavate test pits.
The strategic importance of test pits in the eventual design, alignment of elements, dimensions, workload, extent of a souterrain and perceived functional requirement, needs to be stressed. Much can be learned about the thinking of the tunneller by considering these aspects of a site during modern investigations. Whether it is a ring fort, an ecclesiastic site, an unenclosed surface structure or a surface for which no visible evidence for an immediate surface structure has been identified, considering the issue of ‘test-piting’ allows allows one to gain something of the perspective of the person who created the site. Without completely excavating the surface areas in which clay souterrains are created it is difficult to say how many pits may have been necessary at any one site.
Did the person already understand the nature of the subsoil, was it a man made subsoil level, where a ring fort has a raised surface area ( the result of ‘dead work’), if unknown how many pits provided suitable results for the work to be undertaken, how many pits failed? How were the pits related to each other? What options became evident as a result of the test pit activity? If the cubic quantity of available subsoil was insufficient for the intended souterrain size and design then what alternatives or adaptations were possible at the site? If the surface structure(s) is already in place, then say if the site is a ring fort then is it unsuitable for the souterrain required and consequently should an area beyond the boundaries of the ring fort be considered or could the design be adapted to work with the existence of a ditch and bank; the depth of the ditch might already be an extra indicator of available depth. If the souterrain is created for these reasons outside the boundaries of the ring fort either in immediate proximity or a short distance away, then does this explain why some souterrains appear to be unconnected with the immediate areas of surface structures?
Where the test pit revealed an unequal level of subsoil beneath the required area for the souterrain, then what options were available in preference to relocating the souterrain elsewhere? Two options were available i.e. the use of a limited amount of masonry construction and/or excavating the floors of certain chambers and creep ways, into the upper surface of the rock mantle, something more easily done than tunnelling the whole souterrain into a deeper and more dense level of the rock.
The latter type of adaptability is commonly seen in claycut sites e.g. Corran, County Cork. It is interesting to note that when the intended souterrain form was to be a masonry construction, builders often did the reverse which was to exploit suitable clay levels and even rock, to reduce the quantity of masonry work e.g. the two linked passages to the clay cut beehive shaped cell at Coolgarrif, or the three beehibve shaped chambers, one in masonry the others in clay at Caherdesert; both in Cork. In turn this reduced the amount of quarrying and rock chipping needed for the rubble masonry required for the walls as well as the labour and time element involved in the ferrying of the stone chips from quarry to construction site.
Profile showing a section of glacial till material lying between sod layer at top and bedrock beneath. Note the various levels of gradation in the subsoil profile.
This illustration is an example of the nature of subsoil layers which tunnellers of clay-cut souterrains encountered as they undertook the making of such sites; beginning to excavate from the bottom of the construction pit a floor level at around 2 to 2.5 metres below the surface, and allowing for approximately 60 to 90 centimetres between the chamber ceiling and the surface, dimensions which could be easily determined from a wall profile of the pit.
Were tunnellers familiar with mining and quarrying techniques?
The following is an attempt to profile the process of creating a clay tunnelled site. In the initial phase test pits are used to determine the depth required for horizontal tunnelling and stability of the voids created. Estimations about chamber sizes, location of creeps between them, potential bedrock obstructions, difficulties with interspersed unsuitable subsoil deposits etc could be made using the test pits. Some will become construction shafts, some not. The test pits allow for working out where the usable subsoil deposit lay and what its depths and distribution is across the proposed site for the souterrain. The types of subsoil textures recorded in antiquarian/archaeological reports speak of white stiff clays, sandy clays, dark clays, clay plasticity, large to small pebbles or shale fragments embedded in the clay. The difficulties of working through such textures would need to be understood.
That the tunnellers of clay and rock cut souterrains had some knowledge of mining techniques, quarrying methods and the nature of natural materials in the landscape is evident from their creations. Rock tunnelling – the rock type, state of rock at mantle level, where the bedding planes, how easy to work, how stable, specialised knowledge required of rock types and workabliity – quarries and miners knowledge, any other rock based considerations, dampness and rain water seepage? What to do with extracted soil or rock e.g. spread over the ground nearby, use in construction work or create a mound for grass to grow upon, place in immediate surrounding area of the souterrain or cart to elsewhere for other uses are solutions with which tunnellers would have been well familiar.
Tunnel Construction and the Vertical Shaft as construction shaft
As late the 19th century AD and even today the technique of digging vertical shafts along a sight line from the bases of which horizontal excavation of a tunnel could take place was used in the construction of railway tunnels in the Irish landscape.
The same technique is seen in the woodblock illustrations of Georgio Agricula’s treatise De Re Metallica published in 1556 AD where the tools used are illustrated (Hoover 1912, 150-151). It is an ancient technique and one which is typical of the construction method for clay or rock tunnelled souterrains in South Munster. The process affords two opportunities i.e. it allows for the vertical shaft to act as a test-pit whereby the stratigraphy of rock and subsoil at the site can be assessed in terms of the qualities of the rock and subsoil from a structural viewpoint i.e. can they support a void of certain dimensions without collapsing? What are the limits? How difficult is the material to excavate? What is the depth of the subsoil if the intention is to create a clay-cut site even if this means removal of some of the rock mantle to provide sufficient chamber height through a rock floor and side walls partly rock-cut? Depending on the intended orientation of the souterrain it may be possible to create it in a straight line. However, as it is not possible using test pits to be sure that clay depths remain the same from one pit to another there is an element of chance involved in aligning the tunnel sections from each pit and joining them up. If the actual spread of boulder clay till at one section thins out and rock projects upwards, then this will impact on the work carried out. It may also impact on the direction of, and alignment of, the chambers as well as their forms.
Once tunnelled work has been completed and an entrance shaft to the surface created, be it possible to tunnel one or requiring the use of drystone masonry work, the test pit/construction shafts used to extract the spoil can be backfilled. The process for doing this was to infill the shaft with dry masonry to a level above the opes to the chamber or chambers and then complete the process using soil to surface level. In time the settlement of the soil fill may result in surface depressions above the pits.
At times clever use is made of the masonry work at the base of the pit. At Coppeen East, Cork the pit masonry incorporated a creepway passage from chamber 2 to chamber 4; of interest also at this site was the fact that chambers 2, 3 and 4 encircle from this passage and do not have any construction shaft opes. At Caherdesert near Rathcormack, Cork the pit had a beehive dome masonry chamber constructed within it. At the rock tunnelled site of Curraghcrowley, to the south of Enniskeane in Cork vents which also functioned as chimney flues were constructed within the masonry work of the construction shafts. At Underhill near Kinneigh in Cork a construction shaft was extended on one direction to become an entrance area to the souterrain incorporating ogham stones in its portal frame. There are several other interesting aspects of how the builders of these souterrains, the tunnelled variety , solved their structural issues. Some shafts facilitate two chambers, others facilitate the creation of three chambers as at Brackcloon in Kilcrohane (Cork) and Dunisky near Macroom in Cork. Some chambers do not appear, from current information in the Archaeological Record, to have used any vertical shaft; though this needs re-examination work in the field, even though often sites have been closed off and their precise locations lost to memory. Did some tunnellers, after much experience, burrow out chambers without the need for construction shafts?
It is interesting to note Boyle T. Somerville’s observation in the construction shaft for chambers 4 to 5 at the Curraghcrowley souterrain, that a rock-cut ledge (‘raised platform’) was present. This could have facilitated a labourer taking a spoil satchel from the tunneller and passing it to another labourer on the surface who disposed of the soil nearby or used it elsewhere on site.
Another interesting observation I have recently encountered is that lighting small fires at the base of such vents or flues would heat the masonry exposed in the chamber. The masonry would retain a degree of heat keeping the chamber warm and at the same time providing ventilation. This ties in with the archaeological evidence noted at some tunnelled souterrains where evidence of small fires, some including the bones of small animals have been found. Also, it seems that even up to the 19th century the lighting of fires at the base of vertical shafts as of drawing ‘fresh air’ through a tunnel was practised.
The Lengths of Tunnelled Souterrains
Apart from the fact that collapsed areas are often found, it is difficult to make a statement about tunnelled souterrain lengths. The reason for this is that, quite often, they are not totally linear in their layout i.e. either taking the form of a curved line or a straight line instead they can have chambers at right angles to each other or some parallel to each other. In the table below are the lengths for a three chambered site i.e. Templebryan North, and a larger chambered site at Lisheen. Both of these sites are clay tunnelled.
|SITE||TOTAL LENGTH (Meters)|
The presence at these sites of chamber lengths which are approximately 6 meters long is interesting. Are they simply the result of the structural stability of the glacial till at certain parts of these sites or do they have something to do with the ergonomics of site use? At Lisheen was the 6 meter chamber present as a gathering place for occupying the other chambers (cubicles) as private spaces? Was a place to pray together or take an agape meal?
Rock Tunnelled sites can be as simple as Currahaly which has a length (chambers plus creepways of 17M, or as complex as Dunisky I which has two lengths of chambers and creepways parallel to each other and joined by a chamber (Ch.3) and passage. Furthermore the full extent of this souterrain is not known as a collapsed tunnel at right angles to Ch.1 runs outward beneath the former graveyard area on the surface. a figure for the combined lengths of entrances, creepways and known chambers at Dunisky I would be approx. 50M. There is a notable difference in the tool work between e.g. Ch.3 and Ch.4. The rock has a slatey cleavege in red sandstone this being at the level of the rock mantle, while deeper tunnelling encountered Ch.5.
Excavated volumes of soil/clay removed during creation of a souterrain
|SITE||ESTIMATE OF CUBIC VULUME EXTRACTED (METERS)||MATERIAL|
What was done with the soil/clay or rock removed during the course of the tunnelling work? Occasionally, some recorders have referred to souterrains either within ringforts, or not, as being within, or connected, with low ‘mounds’ or platforms e.g Lurriga, in Abberstrowry. Perhaps in some cases where the souterrrain is either masonry constructed in a trench, or a tunnelled site, the material removed may have been used to increase the volume of surface material above souterrain ceilings thereby offsetting the potential for surface traffic causing accidental collapse. It may also have added a little sound proofing if the souterrain was used as a prayer and contemplation place another possibility is that rock chips were used for masonry of surface structures. In the case of masonry constructed sites it is also of interest to ask what local quarries were used, or created, e.g. small nearby outcrops being cut into chippings for wall construction or slabs for roofing. In terms of estimating the amount of labour involved in a masonry or tunnelled souterrain, the work involved in carting material from a local quarry, as well as in spreading rock, soil and clay extracted during tunnelling work meeds to be factored into the total amount of time, apart from skill levels, involved. The volumes of material extracted to create some of the larger clay and tunnelled sites shows that the creation of at least some souterrains was not an insignificant matter and that significant time and labour as well as planning, site testing and preparation was also involved. These considerations relating to souterrains as construction/tunnelling projects need to be borne in mind also when assessing the creation of masonry constructed souterrains; in particular examples such as Dunbeacon II or the three souterrains at Ballycateen ringfort. Location and placement of the souterrain needs to be assessed the use of clay or rock versus masonry lining for specific segments of a site, quarry sources for chippings and carriage from a quarry as well as subsequent use of spoil extracted.
At this stage of the process practicable decisions need to be made and carried out relating to the construction shafts and where to place them, use of the test pits, which used as construction shafts, which abandoned or put to other purposes later e.g. entrances. The practicalities of passage and chamber alignments needs to be worked out as work progresses as well as modifications and compromises made.
Perhaps actual the chamber shapes and sizes was worked out as work progressed according to structural feasibility. Alignments may have been influenced by structural feasibility as well as requirements for chamber privacy. Ceilings shapes were carved their finished shapes dependent on the textures of rock or clay. Some clays may have large protruding pebbles. Was one chamber to be made larger than the others to serve as a gathering place for prayer and food (agape meal)?
The onsite tools requirement will require hammers, mallets, chisels, picks and spades and also wheelbarrows and carts. A baerlager was the barrow man. Decisions about flooring and depth verses wall height needed to be made, as were decisions regarding flooring on what would otherwise be just rock or damp mud residue, just a scatter of flat stones if wanted or perhaps a layer of intentionally compacted clay.
Further decisions needed to be made regarding the placing of creepways, their directions, whether to use threshold stone only or lintels or jambs in creepways or at chamber entrances ( e.g. Corran South, Cork where threshold stone and jamb were used in the creepway of chamber 4). Decisions to tunnel the souterrain deeper into rock or clay and beneath surface ditches and banks, or running the souterrain out to a nearby natural cave.
Decisions about where drains were to be placed needed to be made, where they would be required or not, where sumps for drains need to be placed, at what distance and gradient, and how the site drain connected to them. Decisions regarding vents and flues needed making such as whether to place them in construction shafts or elsewhere in the ceilings of chambers, how many chambers would need them, if the precise location of the site was intended to be hidden for fear of being discovered and dug out, or the occupants smoked out, where was the surface ope for the vent or flue to be placed in proximity, above or at a distance and in a non-indicative setting? Do those sites which have vents at a great distance from the souterrain e.g, Curraghcrowley, Cork indicate construction during a time of fear from such attacks while those without such features were constructed in more peaceful times e.g. Oldcourt or Fassagh both in West Cork?
At Fassagh (Aghadown) it was suggested that the vents, one per chamber, were used as flues. Was this the intention of the builders or the result of occupants in later times making adaptations to suit their needs?
The question of site construction during times of peace and security versus times of turbulence and violence is perhaps one which might explain a choice of entrance types. Decisions about where and what types of entrance the souterrain should have. Was it to be a simple drophole with a covering slab on the surface? Was it to be a slide shaft also covered with a slab and hidden in a ditch or fence? Was the decision to create a small vestibule chamber inside the entrance to the site a feature of defence or not? Was a porch feature, a surface doorway, or a set of steps an indication that there was no threat envisioned at the time of construction of the site? Or were ogham stones used in some porch features as divine protection?
The outcome of all these decisions are evident as one explores both the survey drawing and as one explores different souterrain forms in Cork.
Cummunication shafts, Flues and Vents Construction:
I have used the word communication shaft on a temporary basis. Such features as found in clay and rock tunnelled sites have a fairly circular cross-section and rise either vertically or at a slight slope to the surface. In diameter they are about 40 centimetres and are closed at surface level with a slab. Examples come from Dunisky and Johnstown both of which two sites are not very distant from each other. At Dunisky the shaft is located in a passage way leading to the original site entrance. At Johnstown the shaft is above one end of the ‘bath’ trough. Were hot stones for a surface fire passed down to boil water in the trough to create steam? Was the Dunisky vertical shaft intended for surface communication with the occupants of the souterrain?
Vents versus flues
Where vents are present in chambers and situated in the masonry work which infills construction shafts, they are usually situated in the upper levels of the masonry work. However at Little Island (Roscarbery, West Cork) Dr. Edward Fahy recorded what were either intended as vents or drains at floor level within the construction shafts. If they were intended as vents how would they have functioned differently from vents placed at ceiling level or near the upper levels of construction shafts? What effect would they have had on air movement within the chamber compared with those at higher levels; as cold air comes in at floor level and warm air rises and exits through ceiling and upper level vents? When discovered this souterrain was filled with water to a level of 15 centimetres. Does that indicate that the ‘vents’ at floor level were in fact placed there to functions as drains?
At Johnstown East the trough or ‘bath’ feature, which was perhaps a later addition to the site, has a stone lined drain in the end wall at the bottom of the trough. What was it intended to drain? Some have suggested that the ‘bath’ might indicate the use of the souterrain as a sweathouse, something common in more northern parts of Ireland but not well referenced if present in Munster. It is interesting to note that the older place name for the townland of Johnstown (Kilmichael parish) was Cill Seanach (cell / hermitage Sheanaigh meaning old cell). If some cill/hermitage sites provided medicinal and care services (spittals) to their local communities, in which the use of sweathouses was a treatment as elsewhere in Ireland, then as a sweathouse the Johnstown souterrain would have been described in Gaelic as a teach allais (healing house?). One also wonders if two other townlands in the parish i.e. aultagh and aultareagh, were also associated with the hermitage and possibly a spittal there; aultagh referencing úll teach (meaning apple cellar or apple house?) and aultaghreagh meaning house made of bundled twigs, illustrious house of the king, or something connected with an apple cellar? It would not be out of place for a cell or hermitage to have úll gorts (apple orchards), lubgorts (vegetable patches), garranes (ploughed fields for crops) or a garraí for animal grazing nearby. How medicinal were apples regarded, considering the tale of Flanaid and Mochuda at Fermoy?
At Curraghcrowley each of the five chambers appears to have had a vent in a construction shaft. Chamber 5 also had a feature which Somerville described as a ‘chimney alcove’. This alcove connected a stone lined vent or flue situated in a trough at 2.74 metres below the surface which ran from the chamber for a distance of 12.2 metres to where Somerville completed his excavations in 1929. However he suggested that the trough may have run on for a further 30.48 metres to a ‘small outcrop where the field level slopes downward steeply’. It is interesting to note that Chamber 5 was considerably blackened with soot, and that there was some evidence of fire or smoke in the vent/flue immediately beyond the chamber. It is also interesting to note that when excavated there was a large deposit of charcoal just outside the main entrance and its rock-cut steps. There was also evidence of blackening in other chambers. Was this souterrain a place whose occupants were smoked out during a raid or period of conflict? Would this explain the charcoal deposit and blackening of walls? Were the chimney alcove and associated external trough designed to off-set discovery of the site by channelling smoke from a light or heat source in the chamber to a location from which the souterrain’s position could not be tracked by raiders with limited time to spare? Did this fail and was the site discovered and its occupants extracted? When might such have happened?
We know that Viking raids for slaves were carried out by the Dublin Norse in the 10th century in North County Kerry for their international market at Dublin. We know that there were several Viking ports and stations along the Irish South Coast and that they raided inland along the major rivers, and perhaps some tributaries. We know that hermitages and monasteries were a target. Curraghcrowley townland is situated in the parish of Ballymoney (Baile na Manach or Manaig meaning homeplace of the monks or lay monks?) a short distance south of the Bandon River. On the north side of the Bandon River lies Laravoolta (beaten up or smashed laura monastery) later rebuilt nearby at Sleenoge townland and famous for its round tower, a focal point of the subsequent medieval monastery and an early bishoprick of Kinneigh. Also in proximity to Kinneigh, in the surrounding civil parishes such as Desertserges and Fanlobbus, several large souterrains have been found, that at Underhill having ogham stones built into the entrance of a clay tunnelled site. Perhaps like the Peake souterrain, north of the River Lee and within the hinterlands of the great Donoughmore monastery of Muskerry, the Curraghcrowley souterrain was part of the monastic hinterland and hermitages of Kinneigh and its Laravoolta.
Were Viking raids responsible for the blackened chambers and damaged skeletons at Peake, and the charcoal deposit as well as blackened chambers at Curraghcrowley? Do both sites represent evidence for Viking raids and their aftermaths?
Illustrations of Vents and Flues – Drawings in progress
Illustrations of Drains – Drawings in progress
Illustrations of Entrances – Drawings in progress
Illustrations of construction shafts – Drawings in progress
This involved finishing off the site for intended use. The construction shafts were closed in with masonry at the opening points to the chambers and the upper portions of the shafts were infilled with soil. Overtime this soil level would settle and it is often the case that depressions in ringfort interiors indicate the presence of a souterrain. Whether or not the entrance was the final part of the construction be it stepped, a box porch feature, a drop hole, a slide shaft or passage, a doorway, a windbreak, a clochán, a hut, a hovel, an oratory was the final stage of the project I cannot say. Once completed the souterrain was then ready for occupancy, or other use, depending on intended requirement. Subsequent modifications may have taken place in later times and perhaps the trough or ‘bath ‘ feature at at Johnstown East is an example of this. Whether or not subsequent uses in later times of certain souterrains turned ceiling shafts in to ‘make shift’ chimney flues is also a consideration.
Masonry Site Construction Process
Like tunnelled souterrains some of the choice of site considerations for a masonry constructed site would have been similar in relation to intended use, site aspect, situation and availability of resources. Whether or not the site need to be totally masonry built and the implications would also be a factor. However, the construction of a masonry site begins with the digging of a trench, not a construction shaft or test pit. The trench will act as the test pit allowing a view of subsoil depth, quality and the nature of the rock surface beneath.
Adaptability and economy of effort: Where to situate the souterrain?
Where the souterrain was to have a dome and passage what decisions regarding the heights relationship between the passage and the beehive dome were made? If the beehive dome is to be built to a significant height above the ‘depth below surface’ of the passage then how to deal with its projection above the ground surface e.g. to locate the domed chamber within the inner face of a ringfort bank, to tunnel part of the passage to a lower depth to allow sufficient underground space to accommodate the dome, to leave the base of the dome at the same level as the passage and then roof the upper part of the dome with a thatch superstructure? Did Ballinacarraige near Fermoy and Ballycateen’s Souterrain C provide evidence for such superstructures? Where the souterrain has two or three domes and was to be located totally underground what clever decisions were made regarding the use of the construction shaft e.g. as at Caherdesert near Rathcormack where the two chambers were cut in clay while the third, the centre chamber was constructed in masonry.
Aspects of masonry construction
Typical of rock and clay tunnelled sites, Oldcourt had no masonry except for its construction shaft. Ahaliskey III had a short square pillar near the entrance which supported a capstone which was less than roof span at this point. Lisnacunna had masonry in the passage only and it had four+ masonry courses visible. Coolgarrif I had a slight outward batter in its passage walls. In the outer passage the lower parts of the walls were clay-cut with a few masonry courses on top of them. This is an interesting combination of techniques which I have not seen recorded for any other site unless one considers the B2 site at Caherdesert III where the construction shaft became a masonry chamber while the other two chambers were clay-cut. At Lyroe I the height of the chamber was the same as that of the passage. The passage only expands in with at one end and this in a sense is the chamber area. There are no creepways or changes in height. It is interesting to consider this site in the context of the A3 souterrain at Rath Townland near Youghal where the sections of passage are not linked by creepways.
Timber work at masonry sites
There were indications of a possible timber structure roofing structure at Ballycatteen, Souterrain C. Was Knockanenagark, Cork something similar in design i.e. one cell with a curved end but without timber roofing? Was the timber roofing at Ballycatteen Souterrain C a later addition to a souterrain which once looked more like Knockanenagark 42km to the north of Ballycatteen?
The Craft of the Corbel Masonry Masters
Corbelling is a masters craft because the mathematics of structural stability need to be understood in order to create a stable beehive shaped dome. So where was it learned and why was it only applied in certain parts of South Munster as far as we know. Why is some of this craft above ground and some underground? Did surface clocháns once have sod covering equating them to corbel domed souterrains below ground? The Cork antiquarian R.R. Brash held the view that they were related. Why was the skill not practiced everywhere in the tribe and clan lands of South Munster? Does the skill reflect the lives and origins of those who came to Ireland or those who travelled eastwards to learn such a craft; compared with those who did not do so and did not try to imitate but used the rectangle instead of the dome for chambers. Did some learn their craft in Syria, in Turkey, in North Africa, in Greece, in Southern Italy where the trulli houses later emerge, in South East France where the borias are found? Are all of these just variant expressions of the same specialised masonry craft at differing stages in time spreading across the shoreline of the Mediterranean from East to West (see Mecca and Dipasquale 2009)?
Raw materials sourcing for masons i.e. workable quarries nearby, carting distance, where to prepare stone chippings for wall construction, suitability of chipped rock for masonry wall courses or for use in a rubble wall construction variant. Availability of suitable tools such as truncated A-frames to create ‘plumb’ internal wall surfaces and to act as formwork during the construction of the masonry walls prior to the placing of capstones on the wall tops, filling the interstices between capstones with small stone chippings and infilling the gap between the external wall surfaces and the trench sides.
Other examples of this type of cleverness and economic use of resources are observable in the use of overlapping capstone layers as at Roovesmore in Muskerry, in the placing of the site entrance in the context of a construction pit at a tunnelled sites as at Underhill near Kinneigh. Such cleverness is a testament to the ingenuity and thinking of the craftsmen creating the site. Another example is from Coolgarrif by Aghabulloge/Donoughmore where the use of both masonry and tunnelling techniques were employed. At this site, apart from the distinction of having two separate passages one linked to the other by a creepway, the chamber was clay tunnelled, the inner passage was partly masonry built while other parts of it and the outer passage were simply the clay cut trench roofed with capstones – immediately beneath which a few courses of masonry were placed to rest the capstones on.
Where no domes are used in the site design the passage may need to be dug to a sufficient depth to allow for the intended height of the chamber to be underground with its floor the same level as that of the passage. The passage as a result may be sufficiently high enough to walk along it rather than crawl while a creepway is then used to distinguish the passage from the chamber. Alternatively, a slight rise in the gradient of the land surface, such as a slight natural eminence or the slope of a hill or a bank may allow for the floors of the passage and chamber to remain at the same level, the height of the chamber being absorbed into the slope or bank. Alternatively the roof of the chamber may need to be project above surface level and become for example a thatched structure. Every souterrain will have its own slight variations in terms of design and modifications according to its specific circumstances and on-site decision making by those who made it.
Preparing the site and what considerations needed
Digging the trench or trenches. Any difficulties with rock outcrops beneath the surface, with subsoil quality and stability of the trench sides? If the trench sections for the chambers or galleries or passages and creepways have to be cut totally in clay is there sufficient depth of subsoil and if not how much rock cutting work is required to make a floor at a suitable depth? How would this decision affect the internal height dimensions and ergonomics within the souterrain spaces?
All excavation work requires the removal of a significant quantity of soil and where necessary a certain amount of rock. This has to be carried and dumped elsewhere. In some cases perhaps it was used to raise the surface of a ringfort interior, in other cases to add an extra surface level over the souterrain such as a mound or platform.
The common practice of masons is to layout a line or lines of construction according to the intended site dimensions. The trench is then excavated. Allowing in width for free space between the masonry work and trench sides wall, construction can then commence. Does he use line and plumb-bob to facilitate the vertical profile and smoothness of the interior wall faces? Does he allow for some corbelling in the upper courses giving a slightly arched appearance to a gallery or passage and if not why not?
Where would the stone chips used in the wall construction come from? How many were prepared onsite or at the quarry? How frequently were randomly collected field stones collected and used? How often were large slabs used either as grounder block in the wall foundations or as orthostats in the wall construction as at Dunbeacon in Cork? How often did the baerlagger and his wheelbarrow ’tend the mason’? There are many questions relating to the motions and activities which would have taken place as the souterrain came into being. What time frame would have controlled it all?
Where was the quarry located, nearby or on site? The question of sourcing suitable stone slabs for the roofing is one which has at times led archaeologists to suggest that burial places were raided for ogham stones at a time when such ogham inscribed stones were no longer respected. This viewpoint then suggests that souterrains are later in date and were built at some time after ogham stones were no longer used as burial markers i.e. mid 7th century onwards. However, if this is the case then why would long ogham stone slabs e.g. such as one from Ballyknock North, Cork not be reduced in size to act as a capstone rather than being left with its inscription intact? Was this just carelessness on the part of the builder or was it because the stone inscription on the stone was respected and intended to offer divine protection to the souterrain space i.e. as a relic? In such circumstances ogham inscribed stones need not be ‘pre souterrain’ in construction date, they may be contemporary. While ogham stones are frequently found in masonry constructed souterrains, a major source of those stone we know of, they are not always present in masonry constructed sites as far as the current archaeological record indicates. Why? Was this because some sites or site types did not require them, was it an indicator of issues connected with the time period in which particular sites were built? How strategic was their placement at some sites e.g. close to entrances, within a specific chamber only etc? Why do some sites have one or two, others 3, some 6 or 10 or 15 such stones either used as capstones and/or pillar-stones to support capstones? Does the use fo many stones indicate a shrine (a ferretory), the use of fewer a hope of divine protection of the site?
Labourers back fill with soil the spaces between outer wall surfaces and trench sides. Interstices between capstones are filled with small chips. The capstones are covered with soil (spoil) and the remaining spoil may be spread over the souterrain to form a slightly raised surface which will to some extent settle and compact over time. The souterrain is now ready for use either immediately or at a future date. Judging by the state of some discovered sites such a future date may never have arrived, as some sites are exceptionally clean, empty of artefacts or evidence of wear or occupancy; in pristine condition one might say. If never used are they an example of over enthusiasm influenced by the desert tradition of Anthony i.e. regarding the need to continue building cells he said ‘build them and they will come’, or is there an other explanation such as a change in religious practice – one as yet unclear? Noting Clinton (2001, 14) and Behon law, the value of two cows as the price for constructing a souterrain must have been significant in a cattle economy.
Studying the Technicalities and allowing the Engineering work to speak
Studying the technicalities of souterrain construction raises many interesting questions about how, where and why souterrains were built in the South Munster landscape; letting the physical evidence of what was done to make these sites to speak for itself. Further study of he technicalities of creating the following Cork sites would be useful i.e. Roovesmore, the expansion of passageway ends leading to chamber creep-ways in Beehive and Passage sites like Manning and Carrignagroghera, those of the Caherdesert beehive domes souterrains, the technical decisions made at the Coolgarrif souterrain in relation to using two passages and only partly using masonry for them, the use of a three openings construction shaft such as at the rock cut sites of Dunisky (McCarthy 2003, 15-30) and Brackcloon (O Riordáin 1934, 78-80), the same at clay tunnelled sites for construction shafts using fewer openings to chambers and their positioning, whether or not some souterrains did not use construction shafts by simply passing the spoil backwards to the entrance, the nature of entrances and reasons for choice on site, clever – and economy of effort – solutions used in the masonry work such as at creepways, the variables of where drains or vents were placed in construction shafts or elsewhere,
This brings the Engineering Chapter to a close. Its purpose was to attempt to profile the construction issues connected with the creation of souterrains as recorded in County Cork and to try and get a sense of the labour, skill and workmanship they represent. The next chapter focuses on the topographies of where the souterrain classes are located. At the present time I’m of the view that the majority of souterrains – and their class designs – are largely of monastic origin and that their topographies, as well as intended functions, are connected with secular christian establishments as well as early medieval monasteries – along with hermitages, dependent or autonomous ones, – as well as demesne landscapes.