The castellated rampart which thus surrounded and guarded Nineveh did not constitute by any means its sole defence. Outside the stone basement wall lay on every side a water barrier, consisting on the west and south of natural river courses; on the north and east, of artificial channels into which water was conducted from the Khosr-su. The northern and eastern walls were skirted along their whole length by a broad and deep moat, into which the Khosr-su was made to flow by occupying its natural bed with a strong dam carried across it in the line of the eastern wall, and at the point where the stream now enters the enclosure. On meeting this obstruction, of which there are still some remains, the waters divided, and while part flowed to the south-east, and reached the Tigris by the ravine immediately to the south of the city, which is a natural water-course, part turned at an acute angle to the north-west, and, washing the remainder of the eastern and the whole of the northern wall, gained the Tigris at the north-west angle of the city, where a second dam kept it at a sufficient height. Moreover, on the eastern face, which appears to have been regarded as the weakest, a series of outworks were erected for the further defence of the city. North of the Khosr, between the city wall and that river, which there runs parallel to the wall and forms a sort of second or outermost moat, there are traces of a detached fort of considerable size, which must have strengthened the defences in that quarter. South and south-east of the Khosr, the works are still more elaborate. In the first place, from a point where the Khosr leaves the hills and debouches upon comparatively low ground, a deep ditch, 200 feet broad, was carried through compact silicious conglomerate for upwards of two miles, till it joined the ravine which formed the natural protection of the city upon the south. On either side of this ditch, which could be readily supplied with water from the Khosr at its northern extremity, was built a broad and lofty wall; the eastern one, which forms the outermost of the defences, rises even now a hundred feet above the bottom of the ditch on which it adjoins. Further, between this outer barrier and the city moat wall interposed a species of demilune, guarded by a double wall and a broad ditch and connected (as is thought) by a covered way with Neneveh itself. Thus the city was protected on this, its most vulnerable side, towards the centre by five walls and three broad and deep moats; towards the north, by a wall, a moat, the Khosr, and a strong outpost; towards the south by two moats and three lines of rampart. The breadth of the whole fortification on this side is 2200 feet, or not far from half a mile. [PLATE XXXVIII.] [Illustration: PLATE 38]