The area's specialty is grapes, and many farms have drying towers for turning them into raisins. Turpan's greenery owes its existence to the underground channels called karezes (or qanats). These underground tunnels rate as one of Asia's more intriguing and historic public works activities (see photograph 3). Uyghur and Chinese versions of karez technology date back over 2,000 years ago.
The qanats of Persia go back to Sargon II (800 bc) and are underground tunnels that carry water. Because they are underground, there is less evaporation of the water.
Written records leave little doubt that ancient Iran (Persia) was the birthplace of the qanat. As early as the 7th century BC, the Assyrian king Sargon II reported that during a campaign in Persia he had found an underground system for tapping water. His son, King Sennacherib, applied the "secret" of using underground conduits in building an irrigation system around Nineveh.
During the period 550-331 BC, when Persian rule extended from the Indus to the Nile, qanat technology spread throughout the empire.