Initially the old tower was converted into a stronger keep which was able to support artillery guns on its roof, a gatehouse was built alongside it, four stirrup towers – so-called because of their shape – a curtain wall was constructed around the outside of the castle, and bastions erected around the wall. Towards the end of this phase of work the castle was altered in a frantic burst of work, possibly driven on by pressure from the King himself. The height of the curtain wall was increased, the gatehouse extended into an entrance bastion, a new network of underground passages installed, and foreworks added around the outside of the bastions. By the end of 1540 the castle was garrisoned with 17 men and equipped with artillery, with Chute appointed as its captain.