Affixed to the north front is the forebuilding, composed of a gatehouse, staircase, drawbridge, and vestibule tower. These formed and protected the entrance to the keep. The approach is thought to have commenced on the west front, near the north-west angle, by a flight of steps, which turned the angle, as at Dover, and were continued as a broad staircase against the wall of the building. Upon this, flush with the west front, was a small low tower, about 12 feet square, through which the stairs passed. This portal had a barred door, but no grate, and its roof was reached from Gundulf’s chamber in the first floor of the keep. From this gate the steps rose to the bridge pit, a cavity 15 feet deep by 9 feet opening. This was crossed by a drawbridge, which fell from the gate of the vestibule tower. The stairs were 8 feet broad, and protected by an outer parapet 2 feet thick and 6 feet high, and probably looped. The parapet crossed the bridge pit on an arch, so that persons ascending the stairs or crossing the bridge were protected.
The vestibule tower is 19 feet broad by 36 feet long, and two-thirds of the height of the main building, against the north face of which, at the east end, it is built. Its walls are 6 feet thick; they have no plinth or pilaster steps, and though probably of the age of the keep the work is of an inferior character. There is a basement, first floor, vestibule floor, and chapel. Each floor is entered from the keep. The basement is 14 feet by 23 feet, vaulted and groined, and it has two air-holes near the vault, ascending obliquely through the wall. The floor is on the ground level, here low, and from it a passage, 2 feet 7 inches wide and 12 feet long, leads up nine stairs into the basement of the keep. The present door from the exterior is evidently not original. This chamber was a prison.
The first floor measures 13 feet by 23 feet; it also has two air-holes, rather larger and less oblique than those below. A recess, perhaps a doorway, perhaps a cupboard, has been opened in the east wall and fitted with a Tudor door-case. This chamber had a flat timber ceiling, forming the floor of the vestibule. It was entered by a passage, 2 feet 10 inches broad, slightly ascending to it from the basement of the keep. This also was probably a prison, but of a less severe character.
The second or vestibule floor is of the same dimensions. In its west wall is the outer door of the keep, of 6 feet opening, round-headed, and flanked inside and out with engaged columns, with plain caps, and round the arch a band of chevron moulding. In the rubble work inside, above its head, is seen a pointed arch of relief. The portal was closed by a barred door only. On the right, on entering the vestibule, is the door of the keep. The vestibule has five windows: a small one in the west wall commands the staircase; in the north wall are three windows, each formed of a pair, coupled; in the east wall is one. They are all round-headed, with Norman ornaments: one-third of the east end of this chamber is covered with a barrel vault.
The third or upper floor of the forebuilding is occupied by the Chapel, the dimensions of which correspond nearly to the rooms below. It is divided into two parts, a nave and chancel, separated by a plain, bold, round-headed arch of 12 feet span. The nave is entered from the main floor of the keep by a side door, close to which, in the wall, is a recess, now inaccessible. The chancel has a stone floor, resting on the vault below, and its roof is three sides of an octagon, also vaulted, a sort of apse, but covering a rectangular space. There are two east windows, and a large stone drain, which has led to the notion that this room was the kitchen, and no doubt it would have made a very good one. The nave had an open roof of low pitch, which was replaced by one perfectly flat, but at the level of the original ridge. If the large upper room in the keep was a chapel, a second would scarcely be necessary. Probably both were not in use at the same time. A kitchen is a very uncommon adjunct to a Norman keep, as the inmates seem to have broiled their meat at an open fire, whereas a chapel is not uncommon; and at Middleham, Dover, Newcastle, and probably at Corfe and Kenilworth, it was in the forebuilding.
The material of the keep is chiefly the rag-stone of the country, with ashlar coigns and dressings of Caen stone. The ashlar is rather sparingly used, but is of sound quality and close jointed. The rubble is poor, imperfectly coursed, and held together by the excellence of the mortar, or rather of the lime, for the mortar is carelessly mixed and is full of sea shells, which have been brought with the sand and left uncrushed. It is clear from appearances, both inside and outside the building, that the south-east angle has, at some period soon after its construction, fallen down, and been rebuilt soon afterwards clumsily and in haste. No mere battering by a ram, no strokes from the missiles of a catapult, however ponderous, would have brought down both turret and wall. Such ruin must have been produced by a mine, and this is the more probable since the south-east is the most exposed angle for such an attack, the scarp of the ditch being here steep, the soil soft chalk rock, and the keep but a few feet from the ditch. A mine opened in the scarp, just outside the angle of the curtain, and driven 40 feet in the chalk, would reach the foundations of the turret, and thus undermined, its fall would bring down more or less of the adjacent walls, and falling outwards, would crush the angle of the curtain. This would account for the large mass of the angle which has fallen, and for the circular bastion tower, evidently an insertion, at the angle of the curtain. Supposing the keep, built in 1126, to have been mined and breached in the memorable siege of 1215, and the damage soon after made good, this would account for present appearances. It is true that the bastion tower is decidedly early English, while the restoration of the keep is Norman, but it is of a period when round and pointed arches were both in use, and when the character of the older part of the keep would naturally lead to the employment of the former; so that the restoration might have been effected as late as 1225, ten years after its probable destruction, and when an entry in the Pipe rolls shows that the sheriff of Kent repaired the tower.
There is a good deal in the character of the forebuilding that looks as though it was an addition to the keep; and yet this cannot be, seeing that the difference in its masonry includes that of the adjacent staircase turret, which could scarcely be an addition. Also the remains of the lower gatehouse, on the north face of the keep, are clearly as old as the keep, of which they are part.
It was long the custom to attribute this keep to Gundulph, making it contemporaneous, or nearly so, with the Tower of London, which it resembles in some of its arrangements, especially its mural gallery and fireplace. Attention to its other details shows, however, that this cannot be so, and that its more probable builder was Archbishop Walter Corboil, about 1126. Those who desire to see examples of Gundulph’s work, and to compare his masonry with that of Rochester keep, should examine St. Leonard’s Tower at Malling, some parts of the nave and transept of Malling Abbey Church, and the north tower of Rochester Cathedral. The White Tower in London has been so often repaired and refaced that it is difficult to be sure of its original masonry. Part of the curtain of the enceinte of Rochester Castle may also be Gundulph’s work. The north wall looks very early, as does the east wall, which is of excellent though rudely coursed rubble, the stones being large and the joints broad, though there are no layers of flat stones as at St. Leonard’s.
Rochester much resembles Hedingham, a very pure and very perfect Norman keep, with three floors, the remains of a forebuilding, and the upper gallery in the main floor. In each ornamentation is effectively employed, and great use made of the chevron moulding. The two buildings are, probably, of about the same date.