The flanking towers are alike, about 22 feet diameter and 55 feet high from the exterior base, with walls 7 feet thick. The bases are either solid or pierced by steps leading down to the galleries. There is a regular basement story, and above it a floor on the level of the inner ward. They are not vaulted and show no exterior herring-bone work, though one has a little inside. A modern summer-house has been built upon that to the south-east. The central or gate-tower is 24 feet diameter. It is pierced at the level of the scarp by a portal which opens upon the drawbridge, the piers of which have been described; and there is a stage above this. The portal ascends towards the keep; its details are much broken down, and little can be made of them. Of the _enceinte_ of the inner ward there remains to be noted the _northern gatehouse_. This, the original and, probably, the only entrance to the Norman fortress, though much ruined, does not appear to have been materially altered. It consists in a rectangular building, 40 feet deep by 20 feet broad, set in the centre of the curtain, with which its outer face is nearly flush. It is crossed by an outer, middle, and inner wall, each pierced by an arch of 12 feet opening, through which lies the passage. There remain the rectangular grooves of a portcullis, and a few years ago there was evidence of a second, and in the wall is herring-bone work. The arches are plain, without moulding or chamfer. The inner one is round-headed, and springs from a flat abacus, chamfered below. The joints of the ashlar work are about 1 inch wide. The curtains on either side of this gateway, though much repaired, seem to be original, and there are traces of the old round gate-towers. The pit of the drawbridge remains in front of the gate, upon the original line of fosse. The outer ward no doubt occupies the site of an earlier outwork. It is built against the narrow and north end of the inner ward, is four-sided, about 250 feet north and south, by a mean of 110 feet east and west. Its west side is straight, being the continued line of that face of the old fortress. The east face has a slight re-entering angle, caused apparently by the shape of the ground. At the two southern angles are two large drum towers, which connect the old and newer work, and probably replace two smaller and older towers. These stand in the line of the old ditch, and flank the Norman gateway. That to the south-west, rather the larger of the two, and slightly oval in plan, has a mean diameter of 60 feet; it is of two stages. Both are vaulted, or rather domed. That to the south-east, of 50 feet diameter, is nearly circular, but has a remarkable spur or keel-shaped projection towards the field. It is of three stages, the two lower being domed. These towers are in fact casemates, having embrasures for small culverins towards the field. Each has a well-stair in its southern side, and is entered from the gorge.