· As early as 3000 BC, a system of irrigation began in Persia called the qanat.
· Qanats 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 qanats to operate in Iran even today.
· Qanats originate in highlands, with a mother shaft as deep as 400 metres, and the tunnel floor slopes at a moderate angle toward its destination, which can be up to 160 kilometres away.
· The difference between the qanat and a surface canal is that the qanat can get water from an underground aquifer, so a surface river or stream is not needed.
· 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.
· The control of water was a key issue to Persian agriculture, and documents demonstrated that Darius and Xerxes authorising the mass construction of qanats at Manâwir in Egypt in an effort to increase agricultural production.
· Polybius claimed that it “granted for five generations to cultivate the lands until the desert regions to those who would bring irrigation to the area… the water which flowed everywhere from the slopes of Taurus.”
· Xenophon claimed that “the canal water was supplied from the river Tigris, and from which the canal ditches were cut to extend over the country.”