aster Mason responsible for the design and construction of Edward I's castles in the north of Wales during the conflict with the Welsh and Llywelyn. King Edward met James whilst travelling in Savoy where he was employed by the counts of Savoy to build castles.. Impressed by his skills in castle building, Edward brought James back to England and by 1278 James was in North Wales working on castles there. Castles that James built include Flint, Rhuddlan, Harlech, Beaumaris and Caernarvon but there are many more. At Harlech he was given the title of constable of the castle.

In the design of many castles he used a concentric plan where a succession of nested walls and towers were built, the walls getting taller towards the centre of the castle. In these castles there are no central keeps, but one or more of the wall towers are large enough to be used in the same way. The gatehouses were also very strong. In the early years of the fourteenth century James was employed in Scotland building castles there as well. His works include Linlithgow Peel, a fortification which replaced a royal manor.

James (of St George's) ( - d.1309)