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]