It is in plan T-shaped, the portal running through the main limb, which projects into the ditch, and the lateral wings, each containing a lodge, forming a gorge or main front of 26 feet width, and flanked by two diagonal buttresses, which cap the angles and project into the ward. Between these is the doorway, and on each side of it a small lancet window, cinquefoil-headed. One of these windows is quite unaltered. The doorway is 7 feet 2 inches broad, with a drop arch and light chamfer moulding. Two feet in is a portcullis groove, succeeded by a doorway of 5 feet opening, of which the valves move inwards. The wall is 4 feet 7 inches thick. The passage is a chamber of two squares, 7 feet broad, and 12 feet 6 inches high. It is vaulted in two equal bays, parted by a transverse rib. Each bay has four hip-ribs, and a straight rib takes the crown line of each vaulting cell, so that eight ribs meet in the centre of each bay, the point of junction being a hollow circle. There is besides a wall-rib in each gable. The rib parting the two bays, and the longitudinal rib, have a plain mitred junction. The rib and circle-mouldings are the same. They are light and bold, 5 inches broad and 7 inches deep. The base of the rib has a hollow chamfer, and its apex is an ogee. The ribs spring from four corner and two intermediate corbels, the tops of which are 7 feet from the ground. These are octagonal and embattled. The bracket below is much defaced. The doorway in the south end, of 4 feet 6 inches opening, had gates opening inwards, and outside them is a second portcullis groove. The lodges open from the central passage close to the ward entrance, by doors, 2 feet 10 inches wide, one of which has the remains of the cusps of a cinquefoil in the head. They are 12 feet broad by 8 feet 9 inches long and 12 feet high, having the small windows already noticed towards the ward. They are hip-vaulted in chalk, with four cells, having four ribs 7 inches broad by 7 inches deep, springing from corbels, now knocked off, but the tops of which were 7 feet above the floor. There are no wall ribs. The portal arches of the main passage are drop in recesses, of which one is so low as to be nearly, and the other is quite, segmental. The vault-arches are equilateral, or nearly so. On each side of the part of this tower that projects into the ditch, on the outside, is a recess, on the west face 4 feet 6 inches, and on the east face 3 feet broad, and 1 foot 4 inches deep. Possibly these were the shoots of garderobes from the upper floor and battlements, now removed. On each side, at the old water level, is a half-arch admitting the water of the ditch below the drawbridge or cradle. [Illustration: TRAITORS’ GATE. ST. THOMAS’S TOWER.—BASEMENT.] In the curtain, close west of this tower, is a well-stair, leading from the west lodge to the roof.