As early as 3000 BC, a system of irrigation began in Persia called the qanat, also spelled quanat. This system is still active today, and has 170,000 miles of active underground canals in Iran alone, and supplies 75% of the water used in that country. 
Quanats are underground tunnels, with a canal in the floor of the tunnel, which carries water. At regular intervals, well-like openings extend from the surface to the tunnel floor, and it is through these openings that the tunnels were built and through which they are maintained. The underground nature of the canal reduces evaporation in the hot and windy desert, and allows 22,000 quanats to operate in Iran today. Many others exist within the sphere of the ancient Persian Empire, which included parts of Turkey, Afganistan, Iraq, Saudi Arabia, Yemen, and parts of the southern former U.S.S.R. Quanats originate in highlands, with a mother shaft as deep as 400 meters, and the tunnel floor slopes at a gentle angle toward its destination, which can be 100 miles away. This aerial photo of Persipopolus, The Persian King Darius' capital, shows several quanat routes. Below is the method of building a quanat.
The difference between the quanat and a surface canal is that the quanat can get water from an underground aquifer, so a surface river or stream is not needed. The quanat tunnel becomes humidified by the water, then further evaporation of water ceases. Since it travels at a slope independent of the surface features, it can go in a straight line. The water carrying canal in qanats were usually lined with stone or tile to reduce water loss.
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