There are exceptional cases in which two mounts occur. At Lincoln (40), the smaller mount is at the south-east corner of the enclosure, and probably may have carried the original donjon. The larger mount, of formidable height and steepness, is west of the centre of the south side. Both mounts, as is usual, are half within and half without the line of the rampart. The stone curtain-wall has been brought up their sides, and the larger mount is crowned by a stone “shell” keep of the late twelfth century. The provision of this second mount was possibly due to the exposed position of the castle, which formed the outer defence of the city on the west and south-west, and needed its greatest strength on that side. At Pontefract and Lewes, again, there were two mounts, one at each end of the enclosure. At both places, the later stone keep was built in connection with the western mount, at the end nearest the town and the slope of the ridge on which it was built. The sites are rather similar, and, in either case, the eastern mount overlooked the river-valley defended by the castle. It is not certain that two mounts ever formed part of an original plan. The natural tendency would be to throw up the mount at first on the side nearer the valley, where the slope was steeper, and the labour required in construction would be less. An attack, however, on the town and castle would come most naturally from the higher ground to the west, which commanded the castle and its defences. A new mount would, in process of time, be constructed on this side, and the old mount would become of secondary importance. At Lewes (50), where the slope of the hill is abrupt, the western mount rises from a higher level, and commands a much wider stretch of country than the mount at the north-east angle of the enclosure. At Lincoln, where an enemy’s force had no advantage of higher ground, the larger mount simply occupies the most advantageous position, protecting the most exposed side of the enclosure, and commanding one of the most extensive views in England. The foot of one mount is little more than two hundred feet distant from the foot of the other; while, at Lewes and Pontefract, the length of the whole bailey lay between the mounts. Thus, while it is possible that, at Lewes and Pontefract, both mounts may be original, with the idea of strengthening the enclosure at either end with a donjon, two original mounts at Lincoln would not have this excuse; and we may infer that, at some date later than the foundation of Lincoln castle, the Norman lords of the fortress threw up a new mount at a point from which the slope of the hill and the approaches from the valley of the Trent could be commanded more thoroughly. [Illustration: Lewes; Plan] [Illustration: Builth; Plan]