Marching camp of 6.2 ha, 4.8 km NW of Rhayader. The
site lies at 420 m elevation on a moorland ridge flanking
the S side of the Gwynllyn valley at SN927699. The
sloping hillside prevented a completely regular plan. The
entrances are represented by four internal claviculae and
the camp could have held up to 4000 men under canvas
on campaign. The objective of their march must by implication have lain in the upper Elan valley, which offers
an easy descent through the Ystwyth valley into the
coastal area of central Wales.
G.D.B. Jones, “The Roman Marching
Camp at Esgairperfedd,” Bulletin of the Board of Celtic
22 (1967) 274.