The walls of the castle are mainly built from ashlar stone, with some red brick used on the south side.[1] The walls are pierced by a small number of gunloops, including in the "ears" of the bastion, which would have overlooked the moat.[44] When first built the interior of the castle formed a sequence of buildings around a courtyard, but the southern half of the castle was filled in shortly afterwards to produce a solid gun platform able to support heavy guns.[45] It was later raised again in the 17th century to its current height.[45] The parapet is now covered with turf, with 19th-century rounded corners, and the platform still has the rails on which the four naval guns would have traversed, dating from 1855.[46] A small lodging room, built on the platform at the top of the stairs, has since been destroyed.[46]