The castle, then, was a Norman importation into England. It was a stronghold with a definite plan, so that the word _castel_ had no vague meaning to English ears. It is found in many cases in close proximity to a _burh_, or fortified dwelling of a community; but it was a royal stronghold, in charge of an individual, and its intention was at once to protect and to keep the _burh_ in subjection. Or, again, it may occupy, as at Tutbury or Conisbrough, the whole site of an early _burh_; but in such cases the character of the _burh_ is entirely changed by the presence of the castle, and the dwelling-place of the community is shifted to the outskirts of the enclosure. At York, Lincoln, and other places where a castle was constructed within part of a _burh_, Domesday tells us that the site was _vastata in castellis_—_i.e._, that houses were taken down to make room for the new earthworks.
A figure of eight, with the lower portion elongated and widened to form the bailey, may be taken as the normal form of the castle plan. Often, as at Berkhampstead (42), where the mount and bailey were surrounded by a broad wet ditch and outer earthworks, the bailey is much the larger portion of the figure on plan; and it was only in small and unimportant strongholds that the bailey formed, as at Mexborough, a mere forecourt to the mount. At Alnwick (115) the mount stood as part of the outer defences of the enclosure, on the slope to the river; but it was so placed that it divided a western or outer from an eastern or inner ward or bailey, and almost filled up the space between them. The arrangement at Berkeley (186) is somewhat similar. If the larger mount at Lincoln (40) were removed to the centre of the present enclosure, and the lines of the curtain-wall returned inwards to meet it, the plan of Alnwick would be obtained. Possibly, however, both at Alnwick and Berkeley, the outer ward may form an extension of the earlier plan, or may have been merely a covering platform, like the outer earthworks at Hastings. The later stone defences have obscured the original designs in both cases.
Although the plan followed fixed and familiar lines, there were no fixed dimensions to the castle. The mount was intended to bear the strong tower or donjon: within the bailey were the ordinary lodgings of the garrison, and such domestic buildings as might be needed. The bailey, which inclined, on the whole, to be oval in form, was surrounded by a low earthen bank, outside which was a dry ditch of more or less depth, with a parapet or counterscarp on the further side. The mount was surrounded by its own ditch, which was joined at two points by the main ditch on the side next the bailey. The entrance to the castle was at the end of the bailey, opposite the mount. These dispositions might vary: the mount might be within the enclosure, even, as at Pickering, in its centre, and the position of the entrance might be different, if the site required it. There might be more than one bailey, and these might be set side by side, divided by an intermediate ditch, as on the fairly level site at Clun (43), or end on end, as on the ridge at Montgomery, or a small bailey might project as a kind of outwork common to mount and bailey alike.[49] The usual arrangement, however, was as described. The mount might be of any height, of enormous proportions, as at Thetford, or of more modest size, as at Brecon or Trecastle. It was usually entirely artificial; but positions were sometimes chosen in which the ground afforded natural help. The mount, for example, at Hedingham in Essex, on the levelled top of which the later square donjon was built, appears to be partly natural; while the great mount at Mount Bures, not many miles away, is wholly artificial. The bailey, again, might vary much in size. It might have a very large area, as at Lincoln and Tutbury, a moderate area, as at Warkworth (49) or Durham (199); or it might be small and compact, as at Trecastle (44). There are many cases, as at Clifford’s hill, near Northampton, where the mount is found by itself: in such instances, the bailey may have disappeared as the result of local cultivation, and only the more important part of the earthworks may have been left. But it is also probable that here and there the fortified mount with the tower on its summit would be all that was needed, and that the absence of a large garrison would render a bailey unnecessary. The size of the bailey, in any case, would depend upon the importance of the position and the size of the garrison required.