Castell Caer Seion is a stone walled fort excavated in 1951 on the summit of Conwy Mountain. It extends over an area approximately 330m from west south-west to east north-east by 100m, having a 'citadel', approximately 65m from east to west by 30m, at the western end. There are some 24 circular structures ranging from approximately 3.0m to 10m diameter located within the enclosures, with others (NPRN 303117 and 303118) without.

RCAHMW AP94-CS 0833-4
RCAHMW AP945114/55; 945115/41; 965001/53-4

J.Wiles, RCAHMW, 4 September 2003.