The approximately 500 m long overflow dam over the Karun, Iran's most affluent river, was the core structure of the Shushtar Historical Hydraulic System ( 3'2G G'? " ( ? 4H4 * 1 ) from which the city derived its agricultural productivity, and which has been designated by the UNESCO as Iran's 10th World Heritage Site in 2009 . The arched superstructure carried across the important road between Pasargadae and the Sassanid capital Ctesiphon.
