The Courtyard - The mound is artificial and this circular "shell" keep would originally have been timber. The stone keep was built in the 12th century (c.1180) and the original medieval stonework can be seen at the base of the lower outer wall which contains an arrow slit and to the left of the doorway into the intra-mural passage is a chute. It is thought this was used in Medieval times to dispose of slops after dark when the entrance door had been locked.
The Shell Wall is 7 feet (2.1 m) thick, 25 feet (7.6 m) high and has a diameter of 106 feet (32.3 m).