Morgraig Castle is located on the crest of Graig Llanishen ridge to the north of Cardiff, positioned on the border between the medieval Welsh Lordship of Senghenydd and the English Lordship of Glamorgan. It is thought to have been raised in the mid-thirteenth century and possibly never completed. The site, which is now ruinous, consists of a rather irregular pentagonal enclosure, about 38m-42m in diameter, defined by walls and towers.
see RCAHMW (2000), Glamorgan Inventory, vol.3 part 1b: The Later Castles from 1217 to the present, p197-208

J.Wiles, RCAHMW, 7 February 2003