Hirllwyn enclosure is a subcircular enclosure, considered to be relatively recent due to the crispness of its banks, the site is sudivided by an internal bank, viewed as integral. Suggested to represent a medieval or post medieval hafod, although an earlier date is not impossible.
(source Os495card; SN83NE7)
ROUGHLY CIRCULAR SINGLE BANKED AND DITCHED ENCLOSURE SOME 25M DIA INTERNALLY WITH INTERGAL SEMI CIRCULAR ENCLOSURE SOME 12.5M DIA IN N PART. ENTRANCE IN SE AND POSS IN NW. MIS-SITED BY Cadw, 1974
Gaps in the outer bank and ditch at the point where they join with the inner, and it is possible the inner ditch was built first, the outer added subsequently. The whole has the appearance of a very small ringwork and bailey, and the earthwork may well be medieval. Its small size and non defensive position, however, suggests that it is more likely to be an embanked farmstead. The preservation is good, the bank retaining an unusually sharp profile. The banks are generally 1m high externally, 80cm internally though the inner bank's internal height in the north is negligible. the ditch is traceable around the eastern half of the river, but is silted up, 2m in width, 30cm deep. Scheduled (Cadw 1994).