The medieval motte or castle mound at Tomen-y-Mur ('the mound on the wall'), is a dramatically mutilated mound set over the north-west gate of the reduced Roman fort (NPRN 95476). It is identified as a medieval castle mound, although documentary evidence is lacking. References to the site seem to relate to the fort in general. The earlier name was Mur Castell. This may have been the site of a medieval llys or princely court.

The tomen is a near-circular steep-sided mound, about 36m in diameter and 6.5m high. The 16m diameter summit has been disturbed in the past. An embanked ditch runs around the foot of the mound. It is built of stone blocks taken from the fort ruins and may conceal a standing Roman gate. The Roman fort circuit appears to have been refortified. Pennant observed ruins of a wall atop the bank in the late eighteenth century. There are traces of post-Roman settlement features to the north-west of the fort (NPRN 89391).

See NPRN 95476 for full photo sources.

Source: History of Merioneth II (2001), 415

John Wiles 11.07.07; T. Driver, RCAHMW, 14th October 2008.