A longhut, associated with a second building and an enclosure, is located on the west side of, and below, the quarry access road through Trefil.
The longhut (at given NGR) is set on a level area platformed into gently rising ground. The platform terrace measures 9.5m long (aligned north-east by south-west), 5.5m wide and cut back to a depth of 0.75m. The building, towards the forward end of the platform, measures 7.5m by 5m overall, defined by broad stony banks 1m-2m wide, widest at the east and west ends, and 0.4m high. Internally the enclosed area measures 3.5m (E-W) by 2m. There is no obvious entrance though the bank is lowest on the north long side.
SO11541407: A short distance to the east of the platform, at the foot of the roadway terrace and on the north side of a stream, is a small rectangular enclosure 5.5m (NE-SW) by 4.5m overall, defined by low stony banks 1m-1.5m wide and 0.2m high. Entrance gap in south corner.
SO11631405: To the south of the above features is a D-shaped enclosure measuring about 15m (N-S) by 15m, defined by a line of boulders embedded in a low stony bank along its east and south-east sides, and elsewhere by a stony bank 1m-1.5m wide and up to 0.4m high. Flanking the enclosure on its west is a linear bank some 25m long (N-S) defined variously by a line of boulders at its south end and elsewhere by a stony bank 1m-2m wide.
(site first noted by F.Olding, Blaenau Gwent Borough Council)

David Leighton, RCAHMW, 25 May 2016