In the design of these castles he dispensed with the traditional keeps and instead used a concentric plan where a succession of nested walls and towers were built, the walls getting taller towards the centre of the castle. As these castles had no central keep one or more of the wall towers were built large enough to be used in the same way. A common feature of James' castles are the strong gatehouses. 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.