A fogou or fougou[citation needed] (pronounced „foo-goo“) is an underground, dry-stone structure found on Iron Age or Romano-British defended settlement sites in Cornwall. Fogous have similarities with souterrains or earth-houses of northern Europe and particularly Scotland including the Orkney Islands. Fewer than 15 confirmed fogous have been found.

Fogous consist of a buried, usually corbelled stone wall, tapering at the top and capped by stone slabs. They were mainly constructed by excavating a sloping trench about 5 ft (1.5 m) wide and 6 ft (1.8 m) deep, lining it with drystone walling as stated, which was battered inwards and roofed with flat slabs; soil from excavation was heaped on top as at Pendeen Vau or incorporated in the rampart of the enclosure as at Halliggye Fogou, Trelowarren.

The purpose of a fogou is no longer known. Their central location in settlements and the work that evidently went into constructing them is indicative of their importance to the community. It has been conjectured that they were used for religious purposes, as refuges, or for food storage. Many are oriented south-west-north-east, facing the prevailing wind. Their use as refuge during raiding trips was first suggested by Darvill in his book ‚Prehistoric Britain‘ (London: Batsford. 1987, page 177). An argument was put forward by Kenneth L MacGregor; was that they mainly served as refuges since food storage is impractical due to the damp conditions and ritual use is unlikely because the Celtic Druid tradition focused more on the living world.

However, being open at both ends, a fogou could provide ideal conditions for food storage, especially the drying of meat[dubious ] or storage of dairy products such as milk, butter and cheese where natural moulds would assist in preservation of perishable foodstuffs. Ashpits found at Trewardreva and in the circular side-chamber at Carn Euny were probably for preserving gulls‘ eggs, as was done on Saint Kilda in Scotland. A layer of black greasy mould with charcoal, animals and bird bones at Treveneague is also very suggestive of food storage. Diodorus Siculus stated that Iron Age people in Britain stored their grain in „underground repositories“, adding contemporary evidence[dubious ] to the speculation that they were mainly used for food storage. Excavated examples at Halliggye, Carn Euny and Boden suggest fogous may have been deliberately filled after use or upon abandonment of the associated settlements.

The word derives from the Celtic *ifócw, meaning „cave“. In the past, locals in Cornwall have called them „fuggy-holes“ but this term is seldom used today.

Tacitus describes the Germans hollowing out underground caves, covering them with manure and using them as storehouses and refuges from winter frosts. He also claimed that they hid in their boltholes to escape detection by raiders, which is one function of the souterrains of Gaul and early medieval Ireland. Fogous may have had a similar function to the underground kivas of Puebloan peoples.

Other underground structures such as „earth houses“ or souterrains have some similarities with fogous. An example of an excavated souterrain is the site at Rosal, Strath Naver, Sutherland. In this example no 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 souterrains could have been used as byres or barns. Fogous are often associated with dwellings such as Iron Age villages.

Petrospheres or „stone balls“ have been found in souterrains and, as possible symbols of power within prehistoric society, this discovery suggest a use other than basic storage of food and resources.

Halliggye Fogou on the Trelowarren estate is generally accepted to be the largest and best surviving fogou.

Other unspoiled fogous survive at Carn Euny, Boleigh near Lamorna, Pendeen and Trewardreva near Constantine, the last of which is known locally as Pixie’s Hall or Piskey Hall.

Partially destroyed fogous exist at Chysauster, which is in the care of English Heritage and which has been blocked up for safety; at Boden Vean near Manaccan and at Lower Boscaswell close to Pendeen.

Evidence of possible former fogous can be found at Porthmeor; at Higher Bodinar; at Castallack and at Treveneague. Another was found during rescue excavations at Penhale Round on the A30, the most easterly example, but this has since been destroyed.