Irrigation. Finding enough water for agriculture, industrial power, and domestic use has always been a problem in the Middle East, where the low rainfall makes the terrain quite different from that of Europe, with its lush forests and abundant rivers. Out of necessity, Arab farmers expanded on many of the technological achievements of the Greco-Roman world and developed efficient ways of moving water from one place to another. Through the use of an elaborate system of gears and wheels for raising and moving water, Arab farmers greatly expanded the amount of land on which they could plant their crops. Use of these devices in Andalusia (Muslim Spain) resulted in the transfer of this technology to Europe. One of the most efficient early tools for bringing underground water to the surface was the saqiya, an animal-driven machine that consists of two gears meeting at...