At the highest point in Gower, 373m OD, Penlle'r Castell occupies the 'pen' (summit) of a mountain formerly known as 'Lle'r Castell' (place of the castle). A purely military stronghold or blockhouse, its position was selected to protect a remote and vulnerable frontier. The form of Penlle'r Castell and the scant traces of its crude masonry permit no firm conclusions as to its date of construction, but its identification with the New Castle of Gower destroyed in 1252 suggests that its foundation, and the encroachment into Gower, did not long proceed that date. No other castle in Gower could have been the New Castle: within the northern uplands of Gower there is only Penlle'r Castell and Cae Castell, a presumed Welsh castle of the 12th century whose form and remote location preclude its consideration as the castle attacked in 1252. For a castle founded c1252 and possibly modified during the next 80 years, Penlle'r Castell is exceptional, not merely in its form, but also for its limited purpose as a purely military frontier fortification incapable of supporting the economic or administrative functions of a castle in more hospitable locations. Its limited function explains its seemingly crude construction and unconventional design. It presumably sheltered a small detachment of mounted men charged with the task of policing a disputed border. (Glamorgan-Gwent Archaeological Trust HER)

The surviving remains consist of impressive earthworks with slight vestiges of the masonry which once crowned them. It has been suggested with reasonable confidence that this unconventional structure was founded by William de Braose II as a military frontier castle c. 1252. (Coflein–ref. RCAHMW, 2000)

Strongly ditched platform with unmortared defences (two square towers?). Not likely to have been a permanent defensive position. No history; believed to be a late C13 strong-point between rival marcher lords