1. Description from Heneb: Dyfed Historic Environment Record (PRN 2733).

Trywn y Castell is a small coastal promontory fort lying on the rocky north Pembrokeshire coast near Abereiddi. The promontory is c. 270m long, E - W, protruding into the Irish Sea. Approximately 140m from its western tip the promontory narrows to 20m. The defences lie across this narrowest point, protecting an area c. 110m by 60m. The defences are multivallate and difficult to understand as they are partly destroyed by erosion on the south side; they consist of several lines of bank and ditch. The outer, eastern bank is the most massive, positioned on a break of slope, it rises just 0.5m externally, is 4m wide and over 3m over the ditch which lies on its inner, west, side. There is no external ditch to this bank. The ditch is rock cut. The bank on the ditch's inner, west, side consists of unexcavated bedrock between two ditches, rather than a built bank. There are two more sets of slight bank and ditch to the west then a gap of 20m. At this point the promontory widens out and is protected by a further bank running along a natural rise. All the banks and ditches stop short of the sea cliffs on the south side of the promontory - the entrance to the fort presumably lay between the defences and the sea cliffs on the south side, although here the topsoil has been eroded exposing bedrock. A post medieval tower lies on the highest point on the interior. To the north the promontory slopes down steeply. On this grassy slope two large hollows below the tower are probably old quarries, but to the west two or three slighter platforms cut into the slope may be the sites of houses.

A sharply defined ditch runs N - S across the promontory approximately 140m east of the fort's defences. This is not an outer defence to the fort but a quarry ditch associated with the workings at Abereiddi. More massive quarry workings to the east of this ditch isolate the whole promontory from the mainland.

K Murphy 15 June 2006

Contains Abereiddi Tower (NPRN 518466) which has been built on the highest point, surmounting an outcrop of rock.