The Clogwyn Arllef Hillfort is an oval enclosure, 70m north-south by 55m, set upon the summit of an isolated ridge and defined by a tumbled stone wall, about 1.8-2.4m wide. The original entrance is towards the northern end of the eastern side and is approached by a ruinous walled lane, extending about 62m to the east. Two small cairns of uncertain purpose, about 5.0m across and 0.4m high, rest immediately within the southern arc of the perimeter. Further similar cairns are reported outside the hillfort to the south on the lower end of the ridge.

Source: Bowen & Gresham 1967 Hist. Merioneth I, 166-7

J.Wiles, RCAHMW, 11 November 2004.