The Nuttall Encyclopedia
Known also as Yird Houses, Weems and Picts' Houses, underground dwellings in use in Scotland, extant even after the Roman evacuation of Britain. Entrance was effected by a passage not much wider than a fox burrow, which sloped downwards 10 or 12 ft. to the floor of the house; the inside was oval in shape, and was walled with overlapping rough stone slabs; the roof frequently reached to within a foot of the earth's surface; they probably served as store-houses, winter-quarters, and as places of refuge in times of war. Similar dwellings are found in Ireland.
Wood, James, ed. Entry for 'Earth Houses'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/e/earth-houses.html. Frederick Warne & Co Ltd. London. 1900.