Morlais Castle was a colossal site but is now buried under its own wreckage and only fragments of masonry can be discerned amid its tumultuous screes. The castle was built amid much controversy by the lord of Glamorgan from about 1288, marking the northern bounds of the newy annexed upland commotes of Senghenydd. It was captured by rebels in 1294 and may never have been restored.

The castle stands on the summit of a high limestone ridge in what was one of the most fertile and productive parts of the Glamorgan uplands. It consists of a great walled enclosure studded with towers, roughly 130m north-south by 60m. The western walls are set above steep slopes and the towers face south and east. At the southern and northern ends were vast round towers, about 20m in diameter, great symbols of lordship that would have dominated the castle's skyline. The fine vaulted basement of the great south tower survives intact. Within the walls are traces of halls and apartments and their associated offices, as well as a great rock-cut cistern.

This great court is surrounded by a massive rock-cut ditch some 15m wide with a counterscarp bank beyond. An outer court on the south side is enclosed only by earthworks. These are cut by the rock-cut ditch and this has prompted the suggestion that the outer court represents the remains of an earlier fortress. However, it is possible that this section of the great ditch has been enlarged and extended through limestone quarrying associated with the adjacent limekiln depicted on the 1st edition OS County series (Glamorgan. VI.9 1875).
Traces of a relict field system to the north-east of the castle have been noted on aerial photography. This could belong to a later period if it is not associated with the castle.

Source: RCAHMW Glamorgan Inventory III.1b The Later Castles (2000) 208-229 [LM10]

John Wiles, RCAHMW, 11 February 2008