On the north, in order to support the later fortification wall, a thick foundation has been laid immediately in front of the palace. The base of this foundation is arranged on the same principle as on the southern side, with separate projecting stepped blocks (Fig. 74). Above this foundation the wall, with its closely set projecting courses, gradually extended so close to the palace wall that it actually touched it (see Fig. 69), and farther up, where they have now perished, the two must have formed one combined wall. From this point the proper towered fortification wall, which still stretches from here eastwards, may have continued on the same line. We do not know, however, in which form it originally extended westward beyond the ancient palace, for here the foundations, as well as the palace itself, were completely destroyed to make room for the junction with the western extension. [Illustration: FIG. 75.—Drains between wall of Southern Citadel and the mud wall. ] Along the north front of the palace there is a walled-in drain which collected the water of the palace and of the top of the fortification walls, and carried it off to the west (Fig. 75). The level of the intermediate space between the palace and the mud wall was originally very deep, but in the course of successive alterations it was gradually raised in about the same degree as the palace pavement. Fig. 75 shows the peculiar construction of these drains. Above the low side walls are placed either plain bricks or moulded bricks of half-moon shape, set edgeways. Larger drains, such as that of the Principal Court or those in the Principal Citadel, are roofed over with corbelled courses, but in these small drains vaulting is obviously avoided. Yet smaller drains were constructed of two flat brick courses placed together at the lower edge and closed in with bricks laid flat, thus forming a triangular section, such as occurs in the north-west corner of Sachn. The top of the fortification walls is regularly drained by means of vertical gutters inserted in the towers; if the towers were built of burnt brick, these gutters are simply carried down inside the towers at a distance of one brick from the front. This kind of gutter is found in the towers on the south side of Nabopolassar’s palace, and in the east part of the north wall. In walls of mud brick, however, it was of course necessary to construct the gutters of burnt brick, and thus the gutter forms a vertical shaft inserted in the mud brick building which surrounds it on three sides (see Fig. 95), while the fourth side lies flush with the outer wall. We shall meet with this remarkable construction, which often attains very considerable proportions, both in the inner and outer town walls, as well as in some of the temples. XVIII THE WESTERN EXTENSION