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.
In the Historia Brittonum written in the the early 9th century, Nennius mentions that a tomb with the inscription "Constantius the Emperor" still stood at the site. Some believe it was the tomb Constantius, father of Constantine the Great. Others believe it could be the tomb of Constantine (not that one) son of Magnus Maximus and Saint Helen.
