The second reason which pointed to the identification is that, in one of the small chambers near the south-west corner of the outer fringe of rooms on those two sides, there is a very remarkable well. It consists of three adjoining shafts, a square one in the centre flanked by two of oblong shape. This arrangement, unique so far as the remains of ancient Babylon are concerned, may be most satisfactorily explained on the assumption that we here have the water-supply for a hydraulic machine, constructed on the principle of a chain-pump. The buckets, attached to an endless chain, would have passed up one of the outside wells, over a great wheel fixed above them, and, after emptying their water into a trough as they passed, would have descended the other outside well for refilling. The square well in the centre obviously served as an inspection-chamber, down which an engineer could descend to clean the well out, or to remove any obstruction. In the modern contrivances of this sort, sometimes employed to-day in Babylonia to raise a continuous flow of water to the irrigation-trenches, the motive-power for turning the winch is supplied by horses or other animals moving round in a circle. In the Vaulted Building there would have been scarcely room for such an arrangement, and it is probable that gangs of slaves were employed to work a couple of heavy hand-winches. The discovery of the well undoubtedly serves to strengthen the case for identification. [Illustration: EASTERN TOWERS OF THE ISHTAR GATE] Two alternative schemes are put forward to reconstitute the upper structure of this building. Its massive walls suggest in any case that they were intended to support a considerable weight, and it may be that the core of the building, constructed over the subterranean vaults, towered high above its surrounding chambers which are on the palace-level. This would have been in accordance with the current conception of a hanging garden; and, since on two sides it was bounded by the palace-wall, its trees and vegetation would have been visible from outside the citadel. Seen thus from the lower level of the town, the height of the garden would have been reinforced by the whole height of the Citadel-mound on which the palace stands, and imagination once kindled might have played freely with its actual measurements.