On the highest ground of the enclosure, near the South-east angle, stands the keep. In grandeur and impressiveness, this tower does not suffer in comparison with any English keep of the Norman period. Neither the smaller keep of Newcastle, nor the larger ones of Colchester, Canterbury, Norwich and Hedingham show the original arrangement better than Rochester. Its base is more than seventy feet square, and it is 113 feet high. It is buttressed at the angles with four small towers each twelve feet square. These, rising twelve feet above the principal mass, add greatly to the picturesque effect of the whole. Clinging like a limpet to the East angle of the keep is a smaller tower twenty-eight feet square and about seventy-five feet high. This contained the chief entrance to the keep. It had a flight of steps and an arched gateway enriched. This and the other arches are constructed of Caen stone brought from Normandy; the walls, from ten to twelve feet thick, are built with Kentish rag. Even when this smaller tower was taken in an assault, the besiegers still had trouble to get into the keep proper, for the vestibule was divided from the rooms of the great keep by a portcullis in the main wall. The groove in which it worked and traces of the ironwork still remain. The keep contains three storeys of lofty apartments, with a vault beneath. As in the tower of London, it is divided into two nearly equal parts by a wall running East and West that rises to the roof. Its thickness allows it to contain a well two feet nine inches in diameter with openings by which each apartment might be supplied with water. By this arrangement, it was impossible for besiegers to cut off the drinking supply of the garrison. The thickness of the walls also admits of mural galleries, as in the White Tower, and a well staircase leading from the vault to the roof, communicating with each apartment. The basement and first floor received their light through loop-holes; the rooms of the higher storeys have their walls pierced with windows. On the second storey were the rooms of state, thirty-two feet high. It has two tiers of windows, the upper tier having a passage in the wall in front of the windows. On this floor, the apartments open into one another through the central dividing wall by four arches; and in the north-east corner is a large doorway leading into an oratory or chapel built over the great entrance. A flight of steps ascends to the wall gallery which goes all round the tower: as in the White Tower, it is vaulted. It is three feet high. In these apartments, there are fireplaces with enriched arches from which the smoke escaped through openings in the wall near the hearth. This primitive contrivance must have rendered the council-chamber and banqueting-hall uncomfortable with draughts.