Construction began for this castle in 1295. It had stopped, with the castle unfinished, by 1300, due to financial issues and trouble Longshanks was having in Scotland because of William Wallace and Robert the Bruce.
Caernarfon was one of the major castles designed by James of Saint George under Edward I. Other castles which he had designed include Harlech, Conwy, and the never completed Beaumaris.