This Burial chamber, a Scheduled Ancient Monument, dates to the Neolithic and is thought to have been in use between 3,500 and 2,500 BCE. It is situated some 125m above AOD, and is located within a rectilinear field, some 15m from its southern boundary. The burial chamber is approximately 350m south of St Andrew the Apostle's Church (NPRN225). Modern aerial photographic coverage and Ordnance Survey mapping show a further stone located within or adjacent to this field boundary, directly south of the burial chamber. Historic Ordnance Survey mapping (1889-1907) depicts this stone approximately 80m further to the south-east.

A cup-marked stone, lying tilted on its side, is thought to have been the burial chamber's capstone. The stone is comprised of silicified sandstone and measures 2 x 2.3m. It appears to have been significantly damaged on one side, and a large stone flake measuring some 40cm x 35cm appears to have been sheared off. A programme of geophysical survey and excavation was undertaken in 2010 by the Welsh Rock-art Organisation, followed by further excavation in 2011 and 2012. A total of five shale beads, thought to date to the Mesolithic, have been discovered to date. 2m north of the stone the remains of a Late Neolithic Grooved Ware pot and an intact human cremation burial were found. Overlying the supposed Neolithic ground surface, immediately south-west of the capstone, the remains of a possible Bronze Age stone burial cist were found. The cist was incorporated into a shale/earth mound, thought to have originally been circular in shape. This was found to contain a vertical cut, suggesting that the stone may have been subsequently erected upright within the cut, as a standing stone. A large amount of white quartz was found to be present around the southern part of the stone, possibly representing the remains of a pavement.

Sources include:
Nash, G, Stanford, A, Therriault, I, and Wellicome, T., 2011, 'Transcending ARTISTIC ritual boundaries,from dolmen to menhir: The excavation of the Trefael Stone, South-west Wales'
National Assembly of Wales, 2009, vertical AP
Ordnance Survey, 1889, First edition 25inch
Ordnance Survey, 1907, Second edition 25inch
www.independent.co.uk, 10 April 2012

N Vousden, RCAHMW, May 2012