Fig. 18.
The rampart was constructed with two faces, of courses of small square stones, with courses of brick at intervals. The masonry between the two faces was of coarse rubble concrete. Outside, along the verge of the plateau, a fosse ten or twelve feet wide protected the base of the rampart and followed the projections of the towers. A narrow covered way was led along the counterscarp to facilitate surveillance and allow the patrol to go their rounds. [Fig. 18] gives the plans of the northern gate with its two towers, at A on the ground level, at B on the level of the curtain battlements. In one of these towers was constructed a stair, C, leading down to a postern, D, and in each of them other flights of stairs, E, which afforded easy access to the higher stories. The gate, divided into two archways for entrance and exit, was surmounted by a gallery, G, at the level of the rampart-walk, forming a crenelation. The road crossed the fosse, F, over an arch, a, and a wooden platform, b, which could be easily removed in time of siege; and then upon the platform, H, a screen of woodwork was to be erected, completely masking the two archways. Outside the bridge, the stonework of which was battlemented, two small uncovered posts, I, defended the approaches, and a palisade, P, obliged all comers to make a circuit in order to cross the bridge. [Fig. 19] shows this gate in perspective. Below the roofing was the crenelation, which constituted the effective defence of the towers. Moreover, at the level of the first story three openings were made, which in time of war were furnished with screens, and which afforded front and side views. Munitions of war were hoisted to the higher stories by means of pulleys suspended in the round-arched openings, K (vide plan of the first story). The other gates were constructed on the same model, the outworks alone being different, according to the disposition of the ground.
Fig. 19
[Fig. 20] gives a general view of the great tête de pont on the south, the place d'armes and the battlemented wall ascending to the square tower on the south angle of the cité, and the castellum. The square towers were not covered by roofs but by platforms, so as to allow catapults or onagri to be placed upon them.[8]
Fig. 20.
With this design quadrangular towers of the kind described were raised at the salient angles of the defences, which were weak points, but which, on the other hand, facilitated the discharge of missiles over a more extensive field. In case a front was attacked, propulsive machines were set up behind the curtains on earthworks or wooden platforms.