Great pains were usually taken to cover the entrances of these keeps by a forebuilding, the details of which have been but little studied. Upon one side of the keep, but a part of its structure, was placed a smaller tower, also rectangular, of the length—that is, covering one side—and about one third of the breadth, of the keep, and two thirds of its height. At one end, at the ground level, commenced a straight staircase which rose to near the other end when it stopped at a landing which was the vestibule of the actual entrance to the keep. Above the lowest part of the staircase was a low tower and a strong doorway. Halfway up the staircase was often a second doorway, and sometimes, as at Dover, a second tower. Over the landing at the stair-head was a larger and taller tower, also with a strong doorway. Outside this doorway the staircase was often broken by a drawbridge, as at Rochester. The staircase was not always covered over, but was protected by an exterior parapet of some height, as at Berkeley, where the shell keep has a forebuilding, a very unusual example. The battlements of the lower or entrance tower were reached by a little door in the adjacent angle of the keep high up. This is seen at Rochester, and at Middleham and Brougham, where the tower itself is removed. In the keep-wall by the side of the staircase was often a recess for the guard, as at Middleham. The bridge-pit had an exterior parapet concealing those who used the bridge. At Castle Rising where the middle gate is perfect, its battlements are reached by a small door from the keep.