The castle is based on Savoyard models where one of the corner towers is enlarged and isolated. This independent structure served as both corner tower and keep or donjon, like at Dourdan, France. Flint's keep has been compared to the donjon at Aigues-Mortes, France. Edward I may have been familiar with Aigues-Mortes having passed through the fortress on the way to join the Eighth Crusade in 1270. An alternative possibility is the influence of Jean Mésot on James of Saint George, Mésot having worked in Southern France before influencing Saint George in Savoy. The castle at Flint has also been described as a "classic Carrė Savoyard" as it is very similar to Yverdon Castle. Its ground dimensions are a third bigger but it shares the classic shape and style, along with the use of a corner tower as keep (donjon). Most historians attribute this to input from Edward's premier architect and castle builder James of Saint George Although construction began in 1277 and James of Saint George didn't begin work at Flint, Flintshire until 1280, he was in England from 1278 and was described as "ad ordinandum opera castorum ibidem" that is charged with the design of the works at Flint, Flintshire