The concentration of military architecture in North Wales from Flint in the east to Anglesey in the west is unsurpassed anywhere in Great Britain. Some of the castles are attributable to the wars fought between the princes of Wales and Edward I of England in 1277, 1282 and 1294/5. Others were built several decades earlier, by both the Welsh and the English. Of these, some were slighted and left in disrepair after Edward's conquest, but the English took over and modified some others, notably Castell-y-Bere, Criccieth and Dolwyddelan. This article is primarily concerned not with them, but with the castles built de novo around Snowdonia by Edward after his various campaigns: Flint and Rhuddlan founded from 1277, Conway, Caernarfon and Harlech from 1283, and Beaumaris from 1295. Their location reflects the outcome of the wars, with Flint and Rhuddlan founded in the east after Llywelyn ap Gruffudd had retreated into Snowdonia; Conwy, Caernarfon and Harlech closer to Snowdon after Llywelyn's defeat and death; and Beaumaris on Anglesey after the Welsh uprising of 1294/5. These castles are judged to be the apogee of military architecture in the late thirteenth century. Imposing and stylish, they represent all that was required in a fortified castle at that time: a visible, formidable presence that dominated its surroundings; defensive strength in walls, mural towers, and gatehouses equipped with multiple port-cullises and murder holes; and domestic apartments suited to the administrative and judicial duties that the constable would dispense in peacetime. The buildings seem to follow a common pattern in planning and detail, which suggests not only that their construction was centrally controlled, but that they were designed by the same architect. A. J. Taylor collected the documentary evidence of central control in The History of the King's Works in 1963; but in 195o he had already affirmed that the architect of the castles was James of St George, Master of the King's Works in Wales. Master James's presence in Wales was already known, but there was doubt whether he was a mason or an administrator. Taylor established unequivocally that he was a mason, and, further, he discovered that Master James actually came from Savoy, where he had been building castles for the counts.