Rectangular Keeps had been prominent in French fortifications for at least thirty years before the Norman Conquest, but the introduction of the defence into England was slow and protracted. Only two examples are extant which preceded the death of William I., namely, the White Tower of London, and the Keep at Colchester. This type of castle has come to be associated with the Normans, to the practical exclusion of the much greater number of Motte and Bailey and Shell Keep fortalices which are equally connected with their occupation; probably the dignified appearance of the massive Keep, with its impressive adjuncts and surroundings, are responsible for the popular belief.
The Keep itself was essentially a new feature in the art of fortification, a medieval method of resisting the special form of attack prevailing at that period. The enclosure was directly derived from the rectangular castra of Roman times, descended through the Anglo-Saxon burh and the Norman bailey. Probably of all the military structures which the world has seen, the Rectangular Keep is the grandest in impressive appearance and dimensions, combined as it is with simplicity of outline; it is also the most durable in workmanship by its adamantine strength and structural proportions. The walls are generally from 8 to 14 feet thick, and, at the base, sometimes even 20 feet, while a few still standing are reputed to have the ground floor solid. The enormous thickness of walls in medieval buildings must not always be taken as an indication of strength; in a large number of cases they consist of two walls at some distance apart, with the intermediate space filled in with rubble and a certain amount of mortar, generally inferior in quality, so that at times when the outer casing is pierced, the interior core pours out through the opening like grain from a sack. They afforded, however, facilities for the construction of passages in the wall itself, and also for small chambers, while the exterior portion of the wall was invariably strengthened by flat pilaster buttresses. The entrances to these Keeps were usually on the first floor, access being gained by means of a ladder or wooden gangway, the doorway being of small dimensions. A series of narrow vertical slits in the walls, splayed out into embrasures inside, served the purpose of windows, and also as oillets or arbalesteria, for the discharge of arrows and bolts.
Later examples of the Keep are furnished with fore buildings adapted to protect the vulnerable portion, the entrance. These fore buildings were especially designed to present unusual difficulties of penetration; drawbridges, meurtriers, oubliettes, and other devices being opposed to intruders, while passages leading to every spot except those desired were constructed in the walls to mislead and divert attacks from inrushing assailants. One of the best examples is that at Newcastle-upon-Tyne, built c. 1172; it has two towers and contains a chapel, the entrance to the Keep itself being from the roof which forms an open platform.
FOREBUILDING OF THE KEEP, BERKELEY.
But by far the best example of a forebuilding is to be found at Dover, standing against the eastern face of the great Keep. It is so designed that three separate protections are afforded to the stairway leading into the Keep, the base, centre, and landing stage having each a separate tower for its defence. The entrance upon the first floor is barred by a door of formidable thickness and great strength; upon the first floor occurs the Chapel, and a view into it is obtained from the stairway, while a small chapel or oratory is placed overhead upon the second floor. A well, now disused, formerly had its opening in the third floor. The actual entrance to the Keep occurs upon the second floor, although an ancient one, now blocked up, opened to it from the first floor.
Dover Castle, from its commanding position at the narrowest part of the English Channel, has for many centuries occupied one of the most prominent positions among the fortresses of England. It stands upon a chalk knoll to the east of the town, and by nature and art is practically severed from the adjacent land, whether high or low. From traces, which are now almost entirely obliterated, it is concluded that a Celtic defence primarily existed upon the summit; this was followed after A.D. 42 by a Roman station, the chief remains of which are to-day embodied in the well-known Pharos, a companion probably to that erected in A.D. 40 by Caligula upon the Gallic shore. Traces of the Roman occupation, apart from the lighthouse, are very scanty, and are overshadowed by the Saxon work, although it is open to doubt whether the development of the latter was carried out to any elaborate extent.
