Known locally as gwal-y-filiast (kennel of the greyhound bitch), this single stone chamber is all that remains of a once much larger burial monument. The name may come from a variant of the Arthurian legend of Culhwch and Olwen, which appears in two fourteenth-century Welsh texts, but the site itself is very much older dating from the Neolithic period, some 5,000 to 6,000 years ago.
St Lythans is a type of monument known as a chambered long cairn and was originally covered by an earthen mound, probably similar to that found at its close neighbour, Tinkinswood. Although the stone chamber is conspicuous as you approach it from the road, the remains of the cairn - or mound - are barely discernible.
It seems to have been about 24 metres (80 feet) long and 11 metres (35 feet) wide with the chamber occupying the eastern end. The chamber now consists of three upright stones with a capstone weighing up to 35 tonnes. How long it was used and who was buried here are questions that remain unanswered but finds of human remains and pottery recovered from the site some time before 1875 were recorded by the antiquarian, J. W. Lukis.