Fitzwilliam’s Tower (18), placed about 80 yards east of the north gate, was connected with a second postern, not unlike the last, and now connected with a caponnière. Beyond this are 19 and 20, two watch turrets, and farther on 21, Albrinci’s or Avrenches’ Tower. This contains a third postern of peculiar arrangement. It is a low, polygonal structure, placed on a shoulder on the ditch, so as to rake its continuation southward. It was reached by a covered gallery from the south gate of the inner ward, which is continued through its basement so as to open on the counterscarp of the main ditch. Connected with this gallery was Veville or Pencester’s Tower, placed upon the curtain which on this side closed the connexion between the two divisions of the outer ward. Of the remaining towers, five in number, three are called Ashford’s, and near one of them was another well. This part of the defence has been completely remodelled. The names of the several towers are those of the knights by whom they were built, or whose duty it was to defend them, for to no castle in Britain, not even to Richmond, was the practice of tenure by castle guard so extensively applied as to Dover, and very numerous and valuable were the Kentish manors so held, amounting to 230½ knight-fees, of which 115¼ were attached to the office of Constable. The _Keep_.—This is a very fine example of a late Norman keep. It is very nearly square, being, at the base above the plinth, 98 feet north and south by 96 feet east and west, with a forebuilding 15 feet broad by 115 feet long, which covers the east side and the south-east angle of the main structure. The angles are capped by pilasters 19 feet broad and of 5 feet projection, which meet to form a solid angle, and, rising to the summit, become the outer faces of four square turrets. On each of the three free faces is an intermediate pilaster, 15 feet broad by 5 feet projection, which rises to the same height with the parapet, and forms a bay in its line. There is a battering plinth, 6 feet high, from which the pilasters rise, and the total height of the wall is 83 feet, and of the turrets 12 feet more, or 95 feet. The base of the keep is 373 feet above high-water mark. The top of the plinth is marked, on the face of the pilasters, by a bold cordon or roll, and there are two sets-off of 6 inches common to both walls and pilasters, one at the first and the other at the second-floor level. The walls are of unusual thickness, even for a Norman keep. That to the west, between the pilasters, is 21 feet reduced to 19 feet at the first and to 18 feet at the second floor. The north wall is 17 feet, the south 19 feet, and the east 18 feet. The cross wall, which runs north and south, and divides the building nearly equally, is 11 feet at the base, and reduced to 7 feet and 6 feet at the top story.