Harold Stone, Skomer
Period: Unknown
An erect monolith, 1.7m high by 0.8 by 0.5m: one of several stones in SW Wales bearing the same name, which seems to derive from Gerald of Wales, who said that the stones were erected by Earl Harold to commemorate his victories over the Welsh in 1063: the relation between this stone and the extensive settlement remains on the island is unclear.
Source: J Wiles 23.05.02 Royal Commision AHM Wales
Whether ancient or not, it certainly is enigmatic on a foggy day!