The tomb at St Lythans was erected during the Neolithic period around 4000-3000 BC. It served as a place of common burial of early-agricultural communities, whose settled lifestyle has allowed them to erect similar buildings. Perhaps it also performed ceremonial functions, as a place of meetings and rites. The bodies of the dead probably remained uncovered before the bones were moved to the burial chamber.
The tomb was composed of a chamber inside a longitudinal mound (cairn) made of smaller stones and earth. The mound was probably about 24 meters long and 11 meters wide, with the chamber occupying its eastern end. Currently, it consists of three vertical stones and a capstone slab acting as a ceiling, weighing up to 35 tons. The capstone, which falls down from the south-east to the north-west, is 4 meters long, 3 meters wide and 0.7 meters thick. The interiors of the two rectangular stones facing each other have been smoothed, and on the top of the triangular back stone there is a triangular opening, similar to those found in other dolmens, such as the Trethevy Quoit in Cornwall. The burial chamber has a minimum internal height of 1.8 meters and is orientated in the east-west line, with the entrance directed to the east.
Website stone-circles.org.uk, St. Lythans Neolithic Chambered Long Barrow.
Website wikipedia.org, St Lythans burial chamber.