[CHAPTER V]
THE SHELL KEEP, c. 1100-1200
The Shell Keep represents the second development of the Norman Castle, and consists of a circular or polygonal ring of stone walling erected upon the motte in the position formerly occupied by the wooden palisading. The substitution of masonry for perishable material was a natural and logical sequence, but in the hurried rush of events immediately following upon the Conquest there was no time for erecting such a defence. A hastily thrown-up mound also would not bear the weight, and it was necessary to allow the earth to consolidate before imposing it. As the country became more settled, and economic and other upheavals less frequent, the Norman barons found time and means to devote to the strengthening of their feudal homes.
Of the precise date of the first Shell Keep erected in these islands we have no definite record; it is very doubtful if any saw the light during the reign of William the Conqueror or Rufus, although many examples could be found at that time upon the Continent. We know that certain Castles, such as Carisbrooke, Lincoln, and Totnes, had developed Shell Keeps prior to the termination of the reign of Stephen, and that Windsor, Berkeley, Arundel, and a number of others were furnished with the same not very long after, so that the age of the Shell Keep may roughly be ascribed to the twelfth century. One must not infer, however, that every example of a Shell Keep dates inexorably from that age, because, having proved its efficiency, it became a recognised method of defence, and Lewes and Durham were endowed with Shells as late as the reign of Edward III.
The Shell Keep is always placed upon a mound, either natural, structural at the time of erection, or a pre-existing motte, but by far the greater number of mounds are artificial. The configuration of the earthwork suggested the shape of the Shell, being either circular, oval, or, as in the case of York and probably Warwick, that of a quatrefoil. The majority are polygonal, the sides not necessarily of equal length, and few of them exceeding the duodecagon in number. The diameter varied from 100 feet to 30, seldom more or less; the thickness of the wall was from 10 feet to 12 feet, and the foundations were carried from 4 feet to 6 feet into the soil. This wall was not built upon the extreme edge of the plateau, but generally a few feet from it and carried upwards to a height of between 20 feet and 30 feet, steps of wood or stone upon the interior face giving access to the rampart.
Being essentially in one compact mass, without vertical breaks of any great extent, and homogeneous in construction, the Shell Keep was specially adapted to crown the summit of an artificial mound. The interior area was occupied by buildings, generally abutting upon the Keep walls; in early examples these were constructed of wood, but subsequently almost entirely of stone to lessen the danger of conflagration.
The substitution of masonry for palisading upon the mound suggested a similar course for the defence of the bailey, and the twelfth century witnessed the erection of many of those gigantic walls surrounding them which excite our admiration at the present day by their massiveness and strength. They followed the scarp of the original mounds, and in many examples the water of the external fosse lapped their bases. The addition of a barbican or ravelin to defend the chief entrance to the castle, which invariably opened into the bailey, was now adopted, while the former wooden ladders or bridges giving from the motte to the bailey were superseded by causeways of stone, defended on either side by a continuation of the bailey enceinte up the slope of the mound. Stone steps instead of wood led from the inner surface of the curtain walls to the ramparts above; stone buildings were erected for the domestic offices, barracks, etc., while the wooden planks and ladders by which the moats had formerly been crossed gave place to masonry arches.
These improvements in the majority of examples did not occur at the same time, hence the presence of a twelfth-century Shell Keep is no guarantee that the curtain walls are of the same age. The introduction of flanking towers, generally semicircular, into the curtain wall, and of rectangular towers, astride it, as a rule, occurred in this century. There are examples in our island, however, which prove that only partial adoption of these improvements took place in many castles, and that, for example, the baron and his family were quite content to dwell within the wooden bretasche upon the motte, at the same time strengthening the weaker bailey defences by the erection of a substantial curtain wall.