The mode in which the walls were constructed seems to have been the following. Up to a certain height--fifty feet, according to Xenophon--they were composed of neatly-hewn blocks of a fossiliferous limestone, smoothed and polished on the outside. Above this, the material used was sun-dried brick. The stone masonry was certainly ornamented along its top by a continuous series of battlements or gradines in the same material [PLATE XXXVII., Fig. 2] and it is not unlikely that a similar ornamentation crowned the upper brick structure. The wall was pierced at irregular intervals by gates, above which rose lofty towers; while towers, probably of lesser elevation, occurred also in the portions of the wall intervening between one gate and another. A gate in the north-western rampart has been cleared by means of excavation, the form and construction of which will best appear from the annexed ground-plan. [PLATE XXXVII., Fig. 3.] It seems to have consisted of three gateways, whereof the inner and outer were ornamented with colossal human-headed hulls and other figures, while the central one was merely panelled with slabs of alabaster. Between the gateways were two large chambers, 70 feet long by 23 feet wide, which were thus capable of containing a considerable body of soldiers. The chambers and gateways are supposed to have been arched over, like the castles’ gates on the bas-reliefs. The gates themselves have wholly disappeared: but the debris which filled both the chambers and the passages contained so much charcoal that it is thought they must have been made, not of bronze, like the gates of Babylon, but of wood. The ground within the gate-way was paved with large slabs of limestone, still bearing the marks of chariot wheels.