Crowning the summit of Carn Fadrun, a prominent mountain on the Llyn peninsula, are the remains of an Iron Age hillfort and medieval castle. The hillfort appears to be of two phases - the first phase enclosing an area roughly 4.8ha in extent and defined by a ruinous rampart wall with entrances to the north and south. The second phase fort enclosed a much larger area, encompassed the first phase fort together with land to the north and south, some 10.7ha. It is defined by a better preserved rampart circuit, again with entrances to the north and south. The interior of the fort shows many tumbled stone-walled buildings, some round, some rectangular and some irregular. Some have small walled yards or gardens attached. Similar features are scattered thickly over the steep slopes below the ramparts and may well represent activity here from the Iron Age through to the Roman period and possibly later.

The medieval castle crowns the highest part of the summit, on the edge of a precipitous fall to the west. Here a narrow platform of rock was utilised as a readymade motte. The ruins of the castle comprise of a narrow loop of drystone wall forming an enclosure below the rocky knoll summit. There are no traces of any internal buildings surviving. Carn Fadrun was mentioned by Gerald of Wales as newly built in 1188, and it forms part of a small cluster of early stone-built castles constructed in Gwynedd at the end of the twelfth century, together with Castell Aber Ia (Castell Deudraeth) (NPRN 302700), Dinas Emrys (NPRN 95284), Tomen Castell (303046) and Castell Pen-y-garn (NPRN 407747). These were not placed to withstand alien invasion, but were rather an expression of a Prince's power and lordship in the unsettled period following the death of Owain Gwynedd in 1170 and the subsequent division of the county between his sons.

Louise Barker, RCAHMW, 5th June 2008