Coastal Iron Age promontory fort, set on south-east shore of Menai Strait.
T. Driver, RCAHMW, 18th May 2009.

'A natural rocky outcrop on the edge of the Menai Strait has been fortified on the landward approach by a crescentic rampart. The rampart slopes downhill from west to east, where much of it has been flattened to form a garden terrace. There is no sign of an outer ditch, nor of any internal structures, although two rectangular stone buildings have been reported here (the site is now very overgrown). The actual habitable area was fairly small, as much of the interior is taken up by the natural knoll (which has probably been reduced in size by coastal erosion). This site has been named as a contender for the unlocated Bon y Dom `castle? built by the King Olaf, Viking ruler of Dublin around AD 1000, as reported in the twelfth century Life of Gruffudd ap Cynan.'
Notes written by Paul Davis to accompany photographs taken in December 2019.