Castell Aber Taf is situated some 150m west-south-west of Trefenty farmhouse (NPRN 17858), and may have been the house's forerunner. Trefenty was the ancient caput of the lordship of Oysterlow (Ystlwyf), which lay mainly between the rivers Cynin and Cywin, and was roughly coterminous with the parish of Llanfihangel Abercowin (whose parish church, St Michael's (NPRN 102138) was situated some 360m south-east of Trefenty farm). Ystlwyf was owned by the Anglo-Norman lords of St Clears until 1171 when it was acquired by Rhys ap Gruffydd. He granted the area to the Cistercian Abbey at Whitland in 1214, as part of the Osterlow Grange. After the dissolution, Sir John Perrot acquired the grange.

Castell Aber Taf is a Scheduled Ancient Monument, consisting of earthworks set along a hog-back ridge, sloping considerably to the south. The castle was first mentioned in documents of 1116. The earthworks comprise a steep-sided oval mound, measuring some 43m east to west by 34m. This has an embanked summit area measuring some 20m across, and a further oval, scarp-defined work set immediately to the east, measuring some 44m east to west by 27m. Historic (1888) Ordnance survey mapping depicts a trackway leading from Trefenty, through the earthwork, to Foxhole. A substantial route is also depicted leading south from this trackway (between Castell Aber Taf and Trefenty) to the reclaimed salt marshes adjacent to the Afon Taf estuary.

Sources include:
www.cambria.org.uk/HLC/EstuaryArea/area155.htm

N Vousden, RCAHMW, 7 November 2012