Bryn Alyn Camp is an elongated enclosure, c.178m fron north to south by 62m, set upon the summit of a promontory all but surrounded by a deep meander of the River Alun. It partly incorporates, and makes use of in its own defences, Wat's Dyke (NPRN 91938). It is defined on the north by three banks and an outer ditch, and by double ramparts facing east. The west side rests on steep slopes above the river. There is a south facing entrance.

Aerial photographs show a further banked oval enclosure springing from the south-east of Bryn Alyn, c.120m from northwest to south-east by 100m, occupying the nab-end of the promontory.

J.Wiles, RCAHMW, 1 December 2003