South Wales was conquered by Robert Fitzhamon, baron of Gloucester, at the end of the eleventh century. The conquered lands included, among others, the Llanblethian, which Robert gave to Herbert de St Quentin around 1102. Herbert was most likely the founder of the first wood and earth fortifications, then expanded at the end of the 12th century.
The castle remained with the St Quentin family until 1233, when it was taken by Richard Siward. The new owner however was declared an outlaw in 1245, and Llanblethian passed to Richard de Clare, Earl of Gloucester and Lord of Glamorgan. His grandson, Gilbert de Clare, began a major rebuilding of the castle when he came of age in 1312. However, these works were discontinued in 1314 due to Gilbert’s death at the Battle of Bannockburn.
In 1317, Llanblethian was granted to Hugh Despenser, the infamous royal favorite, hated by most of the English nobility so much that in 1321 a tense situation ended with the outbreak of the Marcher Lords’ revolt. During it, among others, the castle in Llanblethian was destroyed, although the Despenser family managed to keep it even after the fall of the royal favorite. This allowed for the completion of construction works by Edward Despenser, who died in Llanblethian in 1375.
During the fifteenth century, the gatehouse of the castle was used as a local prison, but in the peaceful sixteenth century, like many other strongholds, the Llanblethian castle lost its importance and fell into decline. In the 18th century it was already largely ruined, but the rooms on the ground floor of the gatehouse were transformed into a residential house, which was used until the 19th century.
The original castle was in the form of a closed, wooden and earth perimeter of the fortifications (ringwork) with a diameter of about 40 meters. They were erected on a hill overlooking the bend of the Thaw River, which provided a strong, natural defense on the north, west and south sides, due to the steep river escarpments. At the end of the 12th century, a stone four-sided keep was built on the elevation of the area. Its sides were probably about 14-15 meters long.
In the fourteenth century, the keep was surrounded by a stone defensive wall about 2 meters thick, delimiting the courtyard on an irregular quadrilateral plan, narrowing on the eastern side. The northern and western curtains were about 60 meters long, while the southern one was slightly shorter, about 55 meters. Additional defense of the castle was provided by a rectangular north-east tower with dimensions of 13.5 x 10.5 meters and a polygonal south-east tower with a diameter of about 10 meters. A much smaller, semicircular turret occupied the north-west corner.
The entrance to the castle was provided from the eastern side by a great gatehouse, consisting of two polygonal towers flanking a 3.2 meter wide passage between them. It was closed with two portcullises located at either end, a door, and had two guard rooms on the sides, each with four cross, oillet arrowslits (including three directed towards the foreground and one towards the gate passage). The northern room was a bit smaller, because next to it in the wall thickness was a staircase to the first floor. The upper floor had only one room heated by a fireplace, although there could have been wooden partitions separating smaller chambers. In the south-west corner of the room there was a latrine, the room was also connected to the adjacent wall-walks of the curtains at a height of 9 meters. Little is known about the appearance of the second floor, probably there were living quarters on it.
To this day, the eastern gatehouse without the highest storey has survived, small fragments of defensive walls and fragments of walls in the place of the former keep, of which only a fragment of the northern wall, about 5 meters high, can be seen. The perimeter wall is best preserved on the north (up to a height of about 2 meters) and west side. Admission to the castle area is free.
Kenyon J., The medieval castles of Wales, Cardiff 2010.
Salter M., The castles of Gwent, Glamorgan & Gower, Malvern 2002.