Building work began in 1277 under Richard L'Engenour, who would later became Mayor of Chester in 1304. The castle and its earthworks were built by 1,800 laborers and masons using local Millstone Grit ashlar and sandstone. In November 1280, the Savoyard master mason James of Saint George began overseeing construction at Flint for Edward I. He remained at the castle for 17 months. James of Saint George then moved onto Rhuddlan to oversee its completion.