The interesting, multi-period earthworks at Pen-y-Castell, Llanilar, occupy the flat summit of a very prominent hill on the south side of the Afon Ystwyth. Pen y Castell is a monument with several phases, not all of which are fully understood. The earliest enclosure on site, a low curving earthwork, is only fully visible on recent airborne laser scanning. This is a large site, measuring 172m N/S by 137m E/W, enclosing 1.7ha. This swings out to the east of main hillfort and is partly covered by gorse. There is the potential for this to be a Bronze Age hillfort, or something earlier given the Neolithic activity below.

Possibly around 400-300 BC a strong, oval Iron Age hillfort measuring c.113m north-south by 60m east-west and enclosing 0.5 hectare, with a well-defined gateway passage on the south-east side which presumably was once the site of a formal walled passage with crossing bridge between the rampart terminals to north and south. There is evidence from the interior that material was quarried around the perimeter to construct the substantial encircling ramparts. During the Iron Age an additional ditched enclosure to the east of the fort (NPRN 400288) may have been added to extend the settled area or to provide a corral for livestock.

Possibly at a later date, potentially when the Iron Age fort had fallen into disuse, a trapezoidal earthwork enclosure was built on the northern slopes of the hill below the fort (NPRN 400287). In the context of the Abermagwr Romano-British villa (NPRN 405315) which lies to the east of Llanilar this defended enclosure could be interpreted as a Romanised farmstead of the period. A geophysical survey of this enclosure was carried out by Archaeophysica LTD for RCAHMW on 26th-27th March 2013.

At a later date the hillfort was effectively cut in two by a deep east-west cutting. Opinion about the date or precise nature of this feature has been divided in the past; A H A Hogg writing in the Cardiganshire County History (1994, 261) considered the hilltop fort to be a prehistoric defended enclosure mutilated by a later quarry or cutting, but J.C. Cathcart-King (1956) interpreted it as the remains of a small medieval motte and bailey arrangement. Hogg and King co-authored a paper in 1963 where they added the following footnote (p.101). 'K [King] accepts as castle, and as probably rightly identified as Garth Grugyn (b 1242, Ann. Camb.). H [Hogg] regards as small fort divided by open-cast cut, and rejects identification as Gareth Grugyn since site lies far outside Crugyn township (now Craigwen).

King's explanation seems more likely, following a field inspection in 2013 by T. Driver and J.L. Davies. The central cutting is neatly cut and bisects the hill in two. It appears to be a deliberate, planned defensive ditch to divide the former hillfort into a motte and bailey, similar to that at Castell Nanhyfer, Nevern, Pembs. A well-defined well or cistern in the north part of the fort looks more akin to the structures found within medieval castles, along with pronounced low wall-footings in the north part which may represent a tower base or rectangular structures.

This neat, likely medieval, rock-cut castle ditch only survives on the eastern side; the west side is further mutilated by a wide quarry cut which takes a large section out of the west side of the fort. It seems likely this is the final phase of activity on the hilltop, with a quarry for building stone possibly cut when Castle Hill house and farm were built. A linear mound of loose material to the east of the ditch cutting cannot be easily explained, but may be quarrying debris from the medieval ditch, a further medieval defensive bank or more recent quarry spoil.

The hill is served by many springs, particularly on the lower hill slopes to the north of the fort. Visited by T. Driver RCAHMW on 9th August 2012 & T. Driver and J.L. Davies on 27th March 2013.

References:
Davies, J.L. & Driver, T.G. 2013, The Villa Hinterland: Recent work on the environs of the Abermagwr Roman villa at Llanafan and Llanilar, Ceredigion, Ceredigion Volume XVII, Number 1. 1-12
Hogg, A.H.A. and King, D.J.C. 1963. Early Castles in Wales and the Marches, A preliminary list. Archaeologia Cambrensis, Vol. CXII (112), 77-124.
Hogg, A. H. A. and Davies, J. L., 1994. Appendix I: Gazetteer of Hillforts and Enclosures. In: Davies, J. L. and Kirby, D. P. eds., Cardiganshire County History. Volume 1, From the earliest times to the coming of the Normans. Cardiff: University of Wales Press. 239-271.