the side entrance to the Throne Room[82] and another doorway in the passage leading to one of the small courts behind it.[83] In two of the chambers within the private palace, both opening on to Court 5, are two more circular wells, walled in for protection, and here too the foundations of each chamber are carried down to water-level and filled in with brick-rubble, as in the case of the wells behind the Throne Room. The same care that was taken to ensure the purity of the water-supply may also be detected in the elaborate drainage-system, with which the palace was provided, with the object of carrying off the surface-water from the flat palace-roofs, the open courts, and the fortification-walls. The larger drains were roofed with corbelled courses; the smaller ones, of a simpler but quite effective construction, were formed of bricks set together in the shape of a V and closed in at the top with other bricks laid flat. The tops of the fortifications, both in the citadel itself and on the outer and inner city-wall, were drained by means of vertical shafts, or gutters, running down within the solid substructures of the towers; and in the case of crude-brick buildings these have a lining of burnt-brick. In some of the temples, which, as we shall see, were invariably built of crude brick,[84] this form of drainage was also adopted. [Illustration: FIG. 11. PLAN OF THE NORTH-EAST CORNER OF THE PALACE WITH THE VAULTED BUILDING. A: East Court of the Palace. B: Central Court. H: Ishtar Gate. I: Vaulted Building. J: Southern fortification-wall of crude brick, probably Imgur-Bêl. _h_: Passage-way leading to the Vaulted Building, _m_, _n_: Entrances to the Vaulted Building. 1-15: Small open courts or light-wells in official residencies. (After Koldewey.)]