At Walmer, where the plan resembles that of the destroyed blockhouse of Sandown (the lunettes being four in number), the embrasures for cannon are still left in their original condition, although certain modern buildings have been erected for residential purposes. Both Deal and Walmer retain the chief part of their original encircling moats. This is a feature of some interest as pointing to a new stage of development in the art of defensive architecture. Hitherto, we have seen that the castles which in Norman times presented flat surfaces to the invaders' engines and battering-rams, were superseded by walls having curved surfaces. Curved walls were still built in Tudor times, and for precisely the same reason as those which were constructed in Edwardian days, but the whole structure of the castle was now depressed within a moated enclosure, the aim being to avoid presenting much surface to the enemy's fire, cannon by this time having become destructive and gunners proficient. [Illustration: FIG. 40. WALMER CASTLE] Sandown Castle was once the prison of Col. John Hutchinson, the regicide, whose life contains a good deal of information as to the dampness and darkness of the place. It stood quite close to the sea-shore about a mile to the north of Deal, and, after being much damaged by the waves, was finally destroyed in 1864. A few indications of its massive strength now survive in a chalky mound. [Illustration: FIG. 41. WALMER CASTLE, FROM THE NORTH] Sandgate was another of this series of blockhouses, its plan being of somewhat triangular form owing to the disposition of three towers in reference to the central tower. It has been much altered in comparatively recent times (1806), and now stands so close to the sea-shore as to be in great danger of being destroyed in due course by the waves. [Illustration: FIG. 42. SANDGATE CASTLE] _Camber._--Beyond the castles opposite the Downs there was one, namely Camber Castle, situated a short distance south-east of Rye, Sussex, which belongs to the same period and was built for the same purpose as the others. Many years ago, however, it had become decayed and useless for coast defence. In 1642 the castle was finally dismantled and abandoned, and the guns were removed. In plan it resembled none of the others of the group, having a central tower and four nearly completely circular towers placed at regular distances around it. Although abandoned for so many years Camber is an excellent example of the kind of blockhouse which was erected by Henry VIII, retaining most of the features unaltered by rebuilding. [Illustration: FIG. 43. CAMBER CASTLE] DEFENCES OF THE ESTUARIES OF THE THAMES, THE MEDWAY, ETC. Another group of defences erected at about this period was designed for the defence of the river Thames, the river Medway, and what in later times came to be known as the Port of London. These included blockhouses at Gravesend, Tilbury, Higham, etc.