Tomen-y-castell is a roughly circular mound, located at the point where the current A494 crosses the Nant Meloch. The mound is bounded by its waters, and those of a tributary, on its north and east sides. It is bordered by the road on the south and a garden on the west, so that if a ditch existed it would have been obliterated. The mound measures some 50m across and 4.0-5.0m high with a level summit some 18-20m across. Tomen-y-castell has been identified as one of a pair of earthworks, the other being Pen uchar'r llan, (NPRN 303428), located some 1.25km to the south-west. Tomen-y-castell is situated 160m east of Bryn-pader (NPRN 43828), which is reputedly the site where travellers first saw St Deiniol's;St Mor's Church, Llanfor (NPRN 43868) and repeated their paternoster. Historic (1889) Ordnance Survey mapping depicts a footpath running south-west from Tomen-y-castell, past Bryn-pader, leading to Ffynnon Deiniol;St Deiniol's well, Llanfor (NPRN 32374) and around the north-west churchyard boundary, where it joins the present road. It is possible that this is a historic route linking the sites.

Sources include:
Beverley Smith, J, Beverley Smith, Ll, 2001, History of Merioneth II, 413
Ordnance Survey, 1889, first edition 25inch

N Vousden, RCAHMW, 19 June 2012