In front of the wall to the north there was water, the moat of the fortress, a part of the Euphrates or of the Arachtu. A sudden assault on the fortress by water might easily be accomplished by means of these canals, and to guard against this huge gratings formed of stone blocks were placed across the channel below the water, thus closing the passage. Every part of the defences, wherever they are intersected by a water-channel, is carefully guarded by gratings either of stone or of burnt brick, to safeguard them against invaders. [Illustration: FIG. 112.—Doorway with canal in the stone wall. ] An assault by means of the water-channel must therefore have been feared by the ancient architects, even if the account of the sacking of Babylon in this manner by the Persians is legendary. [Illustration: FIG. 113.—Canal in front of the Northern Citadel, on the north. ] The wall like that of the Principal Citadel was guarded by alternate narrow and wide projecting towers. The principal wall in the north is clad by a later strengthening wall. The moat, which lay in front of this wall, and which we have also to surmise in front of the eastern wall, was bridged over by a dam which led up to the gentle ascent to the Procession Street. This dam was flanked with sloping walls, of which we have excavated the western one. It bites into the earth with short projecting buttresses. At the northern end a circular cistern was inserted later. Thus the dam led over the defensive moat, and afforded access to the main entrance to the Acropolis. A narrow roofed-in canal led through the dam (K in Fig. 107) and conducted the water from west to east. The roof is laid sloping with bricks placed edgeways (Fig. 113), and like the rubble walls of Nebuchadnezzar it is laid in mud. The technique is the same as that of the canal on the south of the Kasr. Close to the place where the canal turned off from the principal one a brick with the Arachtu stamp of Nabopolassar has been inserted. The canal itself can scarcely be recognised as Arachtu, but we may perhaps conclude from the reverential reuse of the ancient brick that the channel from which this canal branched off bore the name. * * * * * If these descriptions will enable the reader to picture to himself the accumulation of masses of towered defensive walls that guarded the entrance to the Citadel, he will realise that it could hardly have been possible to construct a more imposing approach to this ancient gateway than this one, with its gradual ascent between the walls of the Procession Street, decorated with the long multi-coloured rows of lions, up to the Ishtar Gate and through that to the actual Bab-ilani. XXIX RETROSPECT OF THE KASR