On the Euphrates, where the river-banks are lower, a simple form of water-wheel was probably in use then as it is to-day, wherever there was sufficient current to work one. And the advantage of this form of machine is that, so long as it is in order, it can be unlocked at will and kept working without supervision day and night. The wheel is formed of stripped boughs and branches nailed together, with spokes joining the outer rims to a roughly hewn axle. Around the outer rim are tied a series of rough earthenware cups or bottles, and a few rude paddles are fixed to the wheel, projecting beyond the rim. The wheel is then set up in place near the bank of the river, its axle resting on pillars of rough masonry. The current turns the wheel, and the bottles, dipping below the surface, are raised up full, and empty their water into a wooden trough at the top. The banks of the Euphrates are usually sloping, and the water is conducted from the trough to the fields along a small aqueduct or earthen embankment. Such wheels to-day are usually set up where there is a slight drop in the river-bed and the water runs swiftly over shallows. In order to span the difference in level between the fields and the summer height of the stream the wheels are often huge contrivances, and their rough construction causes them to creak and groan as they turn with the current. In a convenient place in the river several of these are sometimes set up side by side, and their noise when at work can be heard at a great distance.[14]
It is not unlikely that the later Sumerians had already evolved these primitive forms of irrigation-machine, and that the Babylonians of the First Dynasty merely inherited them and passed them on to their successors. When once invented they were incapable of very great improvement. In the one the skin must always remain a skin; in the other the wheel must always be lightly constructed of boughs, or the strength of the current would not suffice to turn it. We have seen reason to believe that, in the palace of Nebuchadnezzar II. at Babylon, the triple well in the north-west corner may be best explained as having formed the water-supply for a hydraulic machine, consisting of an endless chain of buckets passing over a great wheel. Such is a very common form of raising water in Babylonia at the present day. It is true that in some of these machines the wheel for the buckets is still geared by means of rough wooden cogs to the long pole or winch, turned by beasts, who move round in a circle. But it is very unlikely that the early Babylonians had evolved the principle of the cogged wheel, and it was probably not till the period of the later Assyrian empire that bronze was so plentiful that it could have been used in sufficient quantity for buckets on an endless chain. There seems reason to believe that Sennacherib himself introduced an innovation when he employed metal in the construction of the machines that supplied water to his palace;[15] and we may infer that even in the Neo-Babylonian period a contrivance of that sort was still a royal luxury, and that the farmer continued to use the more primitive machines, sanctioned by immemorial usage, which he could make with his own hands.