Thus far the castle is, or has been, a concentric structure, after the plan much in use in the latter part of the reign of Henry III. and throughout that of Edward I. Its peculiarities are caused by the circumstances of its position, and remain to be described. Of these the chief is the keep, or Gloriette, a shell of wall rising from the deep water around it to a considerable height, and containing apartments round a central court, an arrangement usual in Norman shell keeps. This shell contains the chapel, no doubt the “major capella” of the records, the kitchen, and amidst much work of the date at least of Edward I., more that is of that of Henry VIII., and even of recent date. This island is thought to have been the original stronghold of those who first appropriated the spot, but the oldest work now seen dates from Edward I., and the style of the chapel points to about 1280. It contains, however, an excellent low side window, open 17 feet above the water, probably an insertion by Richard II. There is also a postern at the level of the water, part of which appears old, as does an adjacent garderobe. The basement, by which the ground-floor is raised about 12 feet above the water, is solid, and probably very old, for no occupant of these islands for the purpose of security could have neglected this site. Edward, no doubt, remodelled this work with the rest of the castle, and possibly rebuilt the whole of the outer wall. Sir Henry Guildford, custos here for Henry VIII., seems to have removed part of the earlier building, and to have built a spacious hall, a large fragment of which is the present kitchen. During the reign of Charles II. these additions were much injured by fire, so that most of the buildings next the court are modern. Still the general type and arrangement was evidently preserved; and there is little doubt but that this structure represents a late Norman shell, if not an earlier Saxon house of timber. A handsome clock-tower, to which the term Gloriette is sometimes confined, contains a very early clock, and is of the date of Henry VIII., guarding the covered bridge which connects the keep with the larger island. This bridge is of two openings, and has two stories, and was originally a drawbridge, the pit being contained between the side walls, and dropping into the water. It is called in the accounts “pons gloriettæ.”