Souterrain (from French 'sous terrain', meaning 'under ground') is a name given by archaeologists to a type of underground structure associated mainly with the Atlantic Iron Age. These structures appear to have been brought northwards from Gaul during the late Iron Age. Regional names include earth houses, fogous and Pictish houses. The term souterrain has been used as a distinct term from fogou. In Cornwall the regional name of fogou is applied to souterrain structures. The design of underground structures has been shown to differ among regions; for example, in western Cornwall the design and function of the fogou appears to correlate with a larder use.
Souterrains are often referred to locally in Ireland simply as 'caves'. A.T. Lucas, folklorist and Director of the National Museum of Ireland in the 1960s, published a study of the references to souterrains in the early Irish annals. An article by Warner on the archaeology of souterrains, although published 34 years ago, is still possibly the best general overview of the subject. The most comprehensive study of Irish souterrains is Clinton's 2001 work, containing chapters on distribution, associated settlements, function, finds, chronology and no less than thirteen appendices on various structural aspects of souterrains themselves. The book lacks an index. A short summary account of souterrains in Ireland appeared in the quarterly magazine Archaeology Ireland in 2004.
The name comes from the French language, in which it means "underground passageway". In languages other than English, it is sometimes used to mean 'basement', especially in warehouses.
Souterrains are underground galleries and, in their early stages, were always associated with a settlement. The galleries were dug out and then lined with stone slabs or wood before being reburied. In cases where they were cut into rock this was not always necessary. They do not appear to have been used for burial or ritual purposes and it has been suggested that they were food stores or hiding places during times of strife, although some of them would have had very obvious entrances. In Ireland they are often found inside or in close proximity to a ringfort and as such are thought to be mainly contemporary with them, making them somewhat later in date than in other countries. This date is reinforced by many examples where ogham stones, dating to around the sixth century have been reused as roofing lintels or door posts, most notably at the widened natural limestone fissure at the 'cave of the cats' in Rathcrogan. Their distribution is very uneven in Ireland with the most notable concentration centred on County Louth. In Scotland some of them may be connected with the same people who built brochs.
An example of an excavated souterrain is the site at Rosal, Strathnaver, Sutherland. In this excavation, no artefacts or other finds were made inside the structure and the roof may have been only partially covered with stones, a timber roof being present on part of it. It was suggested that the souterrain could have been used as a byre or barn and it was associated with an abandoned settlement.
An example of a partially explored souterrain in northern Scotland, on Shapinsay in the Orkney Islands is Castle Bloody, situated near the seacoast. Another example has been excavated in Perthshire near Alyth.
A well illustrated account of a souterrain excavated at Newtownbalregan, County Louth, one of the many souterrains discovered during the recent road-building programme in Ireland may be found in Archaeology Ireland Winter 2003 issue.
A full report on the excavation of a three-level souterrain at Farrandreg, Co. Louth, in 1998 gives references for the fourteen souterrains previously excavated in this souterrain-rich county. Finds included a rotary quern, a bone comb, a copper-alloy stick pin, three bone needles and the greater part of a tub-shaped pottery vessel in 'Souterrain ware'. The excavator concluded, on the evidence of the finds, that the souterrain had been closed up in the twelfth century.
- Osbert Guy Stanhope Crawford, Antiquity: A Quarterly Review of Archaeology, Published by Antiquity Publications, 1959
- Charles Thomas, Rural Settlement in Roman Britain: Papers Given at a C.B.A. Conference Held at St. Hugh's College, Oxford, January 1 to 3, 1965, Council for British Archaeology, St. Hugh's College (University of Oxford), 1966, 130 pages
- Prehistoric Communities of the British Isles, Greenwood Press, 1971, 274 pages
- Charles thomas, Souterrains in the Sea Province (1972) C.B.A. Research Report 9
- Lucas, A. T. 1971-73 Souterrains: The Literary Evidence, Bealoideas 39-41, 165-91.
- Warner, R.B. 1979 The Irish souterrains and their background, in H. Crawford (ed) Subterranean Britain: aspects of underground archaeology, 100-44. London.
- Clinton, M. 2001 The Souterrains of Ireland. Wordwell, Bray.
- O'Sullivan, M. and Downey, L. Souterrains, Archaeology Ireland, no. 70 (Winter 2004), 34-6.
- Corcoran, W. The souterrain at Rosal, Strathnaver, Sutherland, Proceedings of the Society of Antiquaries of Scotland, 1967-68, 100, 114-8
- C.Michael Hogan, Castle Bloody, The Megalithic Portal, ed. A. Burnham, Nov. 6, 2007
- Coleman, R and Hunter, F 2002 "The excavation of a souterrain at Shanzie Farm, Alyth, Perthshire" Tayside and Fife Archaeological Journal vol 8 (2002), 77-101
- Bailey, D. and Roycroft, N. Souterrain City, Archaeology Ireland, No. 66, 24-7.
- Murphy, D. 2000 Archaeological excavation of a souterrain at Farrandreg, Dundalk, County Louth, County Louth Archaeological and Historical Journal, 24, 2 (1998), 261-80.