Penyrheol defended enclosure (formerly Llwyn-Bwch (south-west)) is a concentric defended enclosure of Iron Age type, with an inner D-shaped enclosure accessed by a single main west gate, and a possible minor postern on the south side. The inner enclosure is contained within an elaborate outer concentric defence which swings out west of the enclosure, and returns back along the south looping back in at the eastern 'rear' of the enclosure almost to form a rounded bastion. The inner D-shaped enclosure measures 76m x 55m enclosing 0.34 hectares, with the outer line of defences expanding the size of the site to a total of 142m x 88m, enclosing 0.8 hectares.

The site occupies a prominent rounded knoll on the west facing slope above the minor river valley, bounded by a stream (now a field ditch) on the north side and by a pronounced dry valley on the south side where the southerly return of the outer enclosure runs. The eastern (uphill) part of the site is wet with several springs. The interior of the inner enclosure has a pronounced hollow inside the main gate. The enclosure is overlooked by high ground to the east, but commands a fine prospect of the upper reaches of the Aeron Valley to the west, and the neighbouring hillfort of Pen y Gaer, Deri-Odwyn (NPRN 303562) to the south. The site was discovered as a cropmark during RCAHMW aerial reconnaissance on 14th July 2003. (Neg ref: 2003/5105-54, 55.) The site was most clearly revealed during aerial photography under drought conditions on 21st July 2006. Earthworks of the western gateway of the defended enclosure as a 1m high earthwork.

Geophysical survey of the site in March 2014 by ArchaeoPhysica LTD clarified the overall plan of the enclosure and discovered the substantial outer line of defence to the south and east, as well as confirming a high amount of activity within the inner enclosure and the sites of possibly two round houses.

The D-Shaped form of the inner enclosure is distinct, and can be paralleled with the univallate Cyncoed defended enclosure at Capel Bangor to the north (NPRN 300149). The enclosure lies only 400m or so west of Sarn Helen Roman road (NPRNs 413964 & 410163), but out of site of the road in a low hollow. It is conceivable that some degree of Roman interaction was experienced by the inhabitants of this later prehistoric site.

Penyrheol will be the subject of an excavation in 2014 lead by Dr. Erika Guttmann-Bond (MIFA) of the University of Wales, Trinity Saint David, with input and advice from Dr. Toby Driver and Louise Barker of the RCAHMW. The project will function as a training excavation for students at the University of Wales TSD, while also focusing on a series of research aims detailed in a Written Statement of Investigation. All work will be undertaken in accordance with the standards and guidelines of the Institute for Archaeologists.

T. Driver, RCAHMW, 2014.