The trapezoidal defended enclosure north of Pen-y-Castell measures 59m from east to west by 56m from north to south, and enclosures c. 0.27 hectares. It was first noted from the ground by J L Davies in 1974.

The defended enclosure occupies a sloping position on the hill to the north of Pen y castell fort (NPRN 303578). The wide spread enclosure bank, with traces of an outer ditch, survives to around 0.4m in height at the north-east corner, reducing to around 0.2m in height for the remainder of the circuit. There is a well-marked gateway at the north-west angle. In general the enclosure incorporates fairly steep hillslope towards its upper (south) end and more suitable, level building sites could have been selected close by. The selection of this particular building site seems to be at least partly related to the high visibility of the enclosure in this position, both to east and west along the reaches of the Ystwyth valley.

With the proximity of the Abermagwr Romano-British villa to the east (NPRN 405315) there is the possibility that this enclosure represents a Romanised defended farm, potentially constructed after the abandonment of the main fort on the summit to the south. A gradiometer (geophysical) survey was carried out for the Royal Commission by Archaeophysica LTD on 26th-27th March 2013.

T. Driver, RCAHMW, 2012 & 2013