A few words must be devoted to an explanation of mottes or mound-castles. These hillocks were essentially low, flat-topped, truncated cones of earthwork, usually surrounded by a ditch, and placed in direct connection with a larger defensive enclosure. The mound was generally artificial, either wholly or in part: the entirely natural mound is the rarest kind[144]. Of these natural hillocks, an illustration is found in the chalk “monticle” on which Corfe Castle is built (Figs. 13, 14). This mound need not detain us, because it is still crowned by the ruins of what was once a solid structure of masonry, built during the reign of Henry I. Of its true character there can, therefore, be no doubt. The castle-mounds which we are particularly considering, in their earlier forms at least, are believed to have supported a kind of wooden guard-house (_turris_, _bretasche_, or keep), which was surrounded by a stockade. Not until a later period of fortification, when the material of the mound had subsided and become firm and solid, did a structure of stone appear on the summit, if indeed, the wooden structure were ever replaced by a more permanent keep or fortress. Stone keeps were built on mottes at Kilpeck in Herefordshire, Fewston in Yorkshire, and other places, but this does not appear to have been the more general custom. Many mounds, at any rate, were never capped by a superstructure of masonry. The castle-mound, as already stated, was encompassed by a moat, which probably, however, was not intended to contain water, except in special cases (Fig. 15). Yet it is very possible that “puddling” was often an undesigned result of the constant trampling to which the ditch was subjected. It should here be explained that the Norman-French term, _motte_, which is constantly applied to the moated mound, is not related to the word “moat,” though, owing to a misunderstanding of the Latinized form, _mota_, it has often been so translated. Beyond the real moat, or ditch, was the larger enclosure to which reference has been made. This was the outer ward, the bailey or base court; it was of horseshoe or crescentic form, and was reached by crossing a wooden bridge. The bailey had its own moat, which, in its turn, was engirdled on the outside by a bank passing along the counterscarp[145]. [Illustration: FIG. 13. Corfe Castle, as it appeared in A.D. 1643. This is a good example of a castle built on a natural eminence. The hill is almost encircled by two streams, which have cut deep valleys, and have nearly severed the mass from the main ridge. A deep, artificial trench on the townward side completes the isolation. ] [Illustration: FIG. 14. Ruins of Corfe Castle, 1910.] [Illustration: