On Gelligaer Common, about 60m to the north-east of a Roman Road formation, lies a post-Roman or Early Christian inscribed stone. As exposed it leans about 45deg. to the north and measures 2.5m long, its section 0.45m by 0.3m at base. It once bore an inscription near the base of its northern face that read NEFROIHI ? ?the stone of Nia-Froich?, apparently commemorating an Irish warrior, and dating to the late sixth to early seventh centuries. The stone was first noted by Edward Lhuyd in 1693, but the inscription is no longer visible.
The stone lies in a water-filled hollow measuring about 3m across at the east end of a horse-shoe shaped enclosure bank that projects away from the stone, possibly the remains of a Bronze Age burial (NPRN 421251).

RCAHMW, Glamorgan Inventory I (iii), p.36 (no.847), PL.2.
RCAHMW AP94-CS 0781
RCAHMW AP945107/42-3

David Leighton, RCAHMW, 8 October 2015