destroyed, but according to Roman custom it seems to have been built with less uniformity than the outer side and shows more clearly the individual handiwork of the separate gangs entrusted (again in accordance with Roman practice) with different parts of the work. Nothing suggests that either buildings or an earthen ramp rested against this inner face. As in other forts of the Saxon Shore, the foundations are very slight, being merely a layer or two of mortared flint tied at one time by wooden stakes. outside were two great V-shaped ditches, the inner 30 ft. wide and the outer about 13 ft. wide, separated from the walls by a berm or platform 35 ft. wide. The unusual width of this berm was due in part to the great height of the walls, whence an easy command of an attack entangled in the ditch-system was requisite. But in part also it was due to the massive towers or bastions which projected at intervals along the walls. At each of the surviving corners stood a round bastion of solid masonry, 18½ ft. in diameter. Each side had apparently three rectangular towers, two of them solid for 8 ft. above the ground and hollow above, projecting 9½ ft. to 10½  ft. and measuring 19 ft. to 20½ ft. in length. Many or all of these were doubtless intended for catapults or other engines of war They are all contemporary with the walls.
   Two gates can still be traced, north and west. The site of the west gate is marked by a gap in the west wall which is mentioned in documents as old as A.D. 1197. The wall trends very slightly inward towards it from each side. The gateway consisted of a single roadway, about 11 ft. wide, flanked by two towers, each about 25¼ ft. by 12¼ ft., projecting a little over 6 ft. from the outer face of the main wall and 8 ft. from the inner. The towers were built, at least as to their lower courses, of massive ashlar, and contained guard-chambers about 16½ ft. by 7¾ ft. internally. The whole plan closely resembles that of the main gateway of the fourth-century fort at Alzei, on the German frontier.³³
   The north gate is far better preserved. It is a postern, incorporated in the central tower on this side, With an elbow-shaped passage barely 4 ft. wide in its outer part. Holes in the walls 15 ft. above its pavement suggest a floor above the passage ; fallen tiles indicate roofing, and a drain passes underneath it. The whole is an effective elaboration of the defensive methods adopted long previously in the designing of the c1avicuIae of the marching-camps. Attacking enemies exposed their left flank to the rampart of the fort ; few at once could reach the narrow opening, and, if that were forced, the elbow in the passage and the widening beyond it still gave a vast advantage to the defence.
   A third gate, postern or other, has been suspected in a corresponding position in the south wall. Here there is a gap, and the foundations have disappeared. The hypothesis therefore remains unproven ; it is not indeed necessary, since late forts like Richborough were often less liberally provided with gates than’ were those of earlier centuries.
   We now pass within the walls. Here a surprise awaits us. Thorough excavation of about two-thirds of the area has revealed scarcely any substantial structure of the period of the fortress. The small triple fortification round the cement platform was levelled, and the filling of its ditches included innumerable fragments of the marble superstructure, which must thus have shared its fate. If further proof of this be needed, it is to be found in the presence, already noted, of marble fragments in the walls of the fortress. In
. ³³ Bonner Fahrbüicher, cxxii, I 36.