How it began
The hydraulic system at Shushtar, in southwestern Iran, can be traced back to Darius the Great in the 5th century BCE, on older foundations. It was designed as a whole and completed in the 3rd century CE under the Sasanians. Its best-known structure, the Band-e Kaisar or "Caesar's dam", is thought to have been raised by Roman prisoners of war and to be the first dam-bridge built in Iran. UNESCO notes that the design drew on Elamite and Mesopotamian knowledge, on Nabatean expertise and on Roman civil engineering.
How it works
Two main diversion canals were cut from the Karun River. One of them, the Gargar canal, is an artificial watercourse that still brings water to the city. A series of tunnels carries the water to mills, and it then falls over a cliff into a basin before running out to the plain south of the city. The ensemble includes the Shadorvan weir and bridge, dams, the Salasel Castle, and a tower for measuring the water level. Wikipedia counts 13 dams, bridges, canals and structures working together.
What changed first
The Gargar canal made it possible to build a new town and to irrigate a vast plain. Orchards and farms were established over an area of 40,000 hectares known as Mianab, which UNESCO translates as Paradise. The same works powered mills and served river transport and the city's defenses.
Where it stands today
The system is still in use. It provides water to the city of Shushtar and supports urban supply, irrigation, fish farming and milling. UNESCO inscribed it on the World Heritage List as a masterpiece of creative genius, and its description notes that the works have served water supply, farming, milling, transport and defense together.
