M. Le Duc, in his Dictionary, Art. “Donjon,” gives a great variety of very curious detail connected with this keep, detail unknown to M. Deville, and for which there should be some authority other than the traces actually existing, which are very unsatisfactory. The keep is built of large chalk flints grouted copiously in mortar, and cased outside with ashlar, now mostly stripped off and removed. Within, the flints are occasionally laid herring-bone fashion. The ashlar was a calcareous tufa, known in the country, and formed by the trickling of calcareous springs over moss and similar vegetation. It was much used in the earlier French castles. The later ashlar of the vaulting ribs and inserted door-cases seems to be a fine hard limestone, approaching Caen stone in appearance, and perhaps actually that material. Where the ashlar is wanting, the putlog holes are seen, placed with exceeding regularity. The joints of the original ashlar are large, those of the later fine. The new and old ashlar can readily be distinguished; but one flint wall is very much like another. The inner ward, in length about 160 yards, and in its greatest breadth about 70 yards, is a natural chalk platform, revetted all round by a wall about 8 feet thick, which on the east side is reduced to a parapet, but on the west rises about 20 feet higher, probably its original height. In 1708 this court contained the apartments of the governor and the staff of the garrison, a well, and a chapel. These were probably of the sixteenth century or later, and have now entirely disappeared. The _enceinte_ wall, which girdles this inner ward, deserves attention, as most of it is of early date. Setting aside the four northern towers with their curtains, which are of later date, we have about 380 yards of curtain broken by five mural towers and three rectangular buttresses. Nearly the whole of the wall is faced with flint, with three bands of ashlar. Much of the flint is laid in herring-bone fashion, the repairs, where of brick, being of much later date. The ashlar bands are of tufa. Of the towers two, half round, are on the east front. Of these one, though probably original, has been cased with brick. The other has had an ashlar base, and the upper part, of flint, shows herring-bone work. Each is about 15 feet diameter, with walls 5 feet thick. Between these towers are three rectangular buttresses; two of 15 feet breadth and 12 feet projection, and one about 7 feet square. The two former contain no herring-bone work, and are probably early additions, perhaps by Henry I.; the latter is original. On the west face are now no towers, but in 1708 there were two, half round, and of small size, traces of which remain. They were, no doubt, original. The remaining three towers capped the three salient angles of the south end, the central containing the gateway, and the others flanking it. All are one quarter engaged.