The keep comprises a central circular tower, in diameter, with six, large solid buttresses projecting outwards to form an hexagonal design, unique in England. It was made from magnesian limestone and tall with walls up to thick in places. It has four floors: a ground floor that serves as a basement and a vaulted stone support for the chamber above; the first floor, through which the keep was accessed; two upper floors and a roof walk, which was probably covered by a pentice and defended by battlements.