Shūshtar, town, southwestern Iran. It is situated on a small plateau below the confluence of the Kārūn River with one of its minor tributaries. Many of the town’s stately houses of stone and brick have cellars, called zīr zamīn, to provide a cool shelter from the powerful summer heat, which may reach the high 120s F (low 50s C). The town was once a major trade centre and dominated an extensive area of irrigated agriculture.
Shūshtar is famous for its great engineering works constructed in ancient times for the disposal and use of the waters of the Kārūn River. Shūshtar’s little plateau sits between the main arm of the Kārūn and an artificial channel more than 100 feet (30 metres) deep, and the city itself is crossed by small canals that use the Kārūn’s water. But the most impressive works are three large dams built in Sāsānian times (224–651 ce) to regulate the river and the artificial channel’s flow and maintain water levels for irrigation. The greatest of these dams, the Band-e Qeyṣar, was originally 1,800 feet (550 metres) long and supported on its numerous arches Valerian’s Bridge, so called because it was constructed under the Sāsānian king Shāpūr I (d. 272) using Roman engineers and other prisoners-of-war captured along with the emperor Valerian in 260. To prevent erosion of the riverbed above the dam, the bed was paved with huge stone slabs bound together with iron. The monumental dam was regarded by later Arab conquerors as one of the wonders of the world. The decay of the dam system in the 19th century spelled the collapse of both Shūshtar’s irrigation network and its prosperity, although several waterwheels on the canals are still used to drive numerous small flour mills and to generate electricity. The historic hydraulic system has been honoured as a masterpiece of creative genius and recognized by UNESCO as a World Heritage site. Pop. (2006) 96,732.