The inner wall is a box rampart. Two lines of wooden uprights, joined at top and bottom form a series of boxes, filled with rubble for strength. The front of the box is vertical and faced with dry-stone walling. It stands 18’ high and is topped by a 3’ high dry-stone wall breastwork, and is backed with a sloping rampart of earth and rubble almost 30’ wide, adding strength and rigidity to the inner wall. The ramp also provides the defenders easy access to the battlements. The western, landward, side of the fort has two additional walls that are not surmounted with a palisade, but have a ditch between them.