32.0441°N, 48.8584°E.
The Shushtar Historical Hydraulic System is a network of dams, weirs, tunnels, mills, bridges, and canals on the Karun River in Khuzestan Province, southwestern Iran, attributed in its surviving form to Sasanian engineers of the 3rd century CE under Shapur I, with Achaemenid antecedents and continuous Islamic-era extension into the Safavid period. The system splits the Karun into two channels — the natural Shutait and the artificial Gargar — using the Band-e Kaisar weir-bridge, a structure long credited to Roman prisoners taken at the Battle of Edessa in 260 CE, when the emperor Valerian was captured by Shapur. A cliff face downstream at Shushtar is honeycombed with rock-cut tunnels that drove a cascade of water mills grinding grain for the surrounding plain, then released the spent flow as a stepped waterfall into irrigated orchards and back to the river below.
" The Shushtar Historical Hydraulic System is a working machine carved into bedrock that still operates seasonally seventeen centuries after Shapur signed the order.