Criccieth castle was first built as a centre for Eifionydd commote by Llywelyn ab Iorwerth, probably in the 1230s, and Llywelyn ab Gruffudd is thought to have enlarged it in the later thirteenth century. It was captured by the forces of Edward I in 1283 and a large sum of money was spent on building work before the castle was besieged during the troubles of 1294-5. Further works were carried out in the earlier part of the fourteenth century. The castle was taken and destroyed in 1403-4 and was never rebuilt. The castle occupies the summit of an isolated crag washed by the sea on the south. The borough, chartered in 1284, probably occupied the dingle separating the castle crag from the rock of Dinas to the north-west (see NPRN 33014).

There is some controversy about the sequence of building and the following summarises the most recent interpretation. The original castle is a polygonal walled court about 35m north-south by 30m. At the north end is a great twin towered, three storey gatehouse, on which is a large rectangular tower on the south-east side. By the end of the century there was a great hall in the court. Llywelyn ab Gruffudd added walled courts on the north and south-west, each with a large rectangular tower. The entrance was in the south-west court, reached by a track winding around the castle rock. A long narrow passage connected the outer courts. This plan of separate courts each with their own great tower is reminiscent of the contemporary Ewloe Castle (NPRN 94447). The late thirteenth-earlier fourteenth century work is thought to have involved raising or rebuilding the towers. This can be seen in the fabric of the great gatehouse. Lower down the castle rock there is a rock cut ditch on the north and north-east, and an outer rampart skirts its base. These works are undated.

Sources: O'Neil in Archaeologia Cambrensis 98 (1944-5), 1-51
RCAHMW Caernarvonshire Inventory II (1960), 59-62
Johns MPB&W Guide to Criccieth Castle (1970)
Gresham in the Transactions of the Caernarvonshire Historical Society 34 (1973), 14-22
Avent CADW Guide to Criccieth Castle (1989)

John Wiles, RCAHMW, July 2007.