Near the summit of Cefn Gelligaer is a spread, damaged round cairn capped by a triangulation pillar. The cairn is slightly oval and measures 19.5m (east by west) by 15.8m with a height of about 1m, but 1.5m on the north-east, downhill, side of the cairn. The cairn is set within a partly visible kerb of massive outward-leaning slabs, most clearly exposed on the south and south-east where they are 1.2m-1.5m long. Here, just beyond the kerb are some dislodged slabs lying flat. These are possibly remnants of an outer ring though there is some evidence for an inner ring also on this quadrant. At the centre is a hollowed area 3m (east by west) by 2m. At its south edge is an oval slab 1.9m by 1.4m, the capstone of a former cist of which only the south-west end-slab is now visible.
Eighteenth and nineteenth century diggings here reported finds of "bones and urns" and three three parallel cists.
refs:
RCAHMW, Glamorgan Inventory vol.1 pt 1 (1976), p.70 (no.156).
RCAHMW AP945107/44-5.

David Leighton, RCAHMW, 15 October 2015