The vestibule at the stair-head was usually a good-sized chamber, often vaulted. In it was the main doorway of the keep, of not less than 6 feet opening, with flanking shafts and moulded architrave. At Castle Rising this ante-chamber is arcaded, and very handsome; at Rochester it is plain, or nearly so. At Dover it contains a guard-chamber, at Newcastle and at Middleham a chapel. The basement below the vestibule was usually a prison, and had a small door into the corresponding basement of the keep. At Rochester are two floors below the vestibule and two above it. The forebuilding is perfect only at Castle Rising, Norwich, Dover, and Newcastle; there are large remains of it at Rochester, Porchester, and Middleham, and some at Hedingham, Corfe, and Kenilworth. At Scarborough, Brougham, Bramber, Canterbury, and Helmsley there are traces only. At Dover there are vaults below the staircase and lower tower, above which is a vestibule and a chapel, and in the first or upper floor a second chapel. Sometimes there is a way from the foot of the staircase of the forebuilding into the basement of the keep, but probably this is not original. It is seen at Dover, Newcastle, and Castle Rising. The White Tower has been so pulled about that it is difficult to say how it was originally entered. The forebuilding is essentially a Norman appendage, and, with the exception of Berkeley, and, perhaps, Chilham and Orford, confined to keeps of the rectangular pattern. It has been supposed to mark a late keep, but there is a forebuilding at Arques usually regarded as a very early one.