In the houses 28, 29, 30, a large chamber is interposed between the court and the usual principal room lying to the south of it. This additional chamber is a hall that opens with a wide arch on to the court. This must have been a very pleasant room in summer, for the entrance lies all day in shadow. These halls opening with wide arches into the court played a prominent part in Parthian and Sassanide times in the ground-plans of Ktesiphon, Hatra, Assur and other towns of that period, especially in the palaces; and as _liwan_ they now play an important part in modern oriental architecture. Visitors to Mossul, Aleppo, and many other cities have a vivid recollection of them. Here in Babylon the idea shows itself tentatively and timidly. The houses 13, 14, and 16 have similar rooms. In 25, 26, 27, the entrance hall opens in _liwan_ fashion on to the court. We can here observe the uncertainty that attends a new idea, which only after the course of centuries, and not without reiterated fertilisation from the west, has at last emerged into glorious fruition. In the north-west corner of the Principal Court a broad passage guarded by a series of three arched doorways leads to a gate in the city wall. Here the eastern portion of the Citadel wall, with its closely set towers, adjoins the western portion, of which only the foundations remain which show no traces of towers. In the passage is a large drain, roofed over with corbelled brick courses, which carried off the surface water from the Principal Court through the door in the wall past the palace and then farther west to the Euphrates. The same drain also branched off to the south, down through the southern wall of the Citadel, where, as the wall was already in existence, an outlet was cut for it. Thus it had a fall to the north and another to the south. [Illustration: FIG. 67.—Ramps between the Nebuchadnezzar and Nabopolassar Palaces. ]