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" meaning 'cave'. In Cornwall the regional name of "fogou" (Cornish for 'cave') 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.