Shushtar is a historical city located in the southwestern part of Iran, in Khuzestan Province. It is situated on the banks of the Karun River and is known for its ancient hydraulic engineering system, which is considered a masterpiece of ancient engineering.

The hydraulic system of Shushtar, also known as Shushtar Historical Hydraulic System, includes a series of water mills, dams, bridges, tunnels, and canals that were built during the Achaemenid and Sassanid periods of ancient Persia. The system was designed to supply water for irrigation, drinking, and industrial use, and is considered an outstanding example of the ingenuity of ancient Persian engineers.

The hydraulic system consists of several parts, including the Gargar Canal, which is the main canal that carries water from the Karun River to the city, and the Shadorvan Bridge, which was built to cross the canal. Other important structures include the Band-e Mizan Dam, the Band-e Kaisar Dam, and the Salasel Castle, which served as a fortress to protect the city from enemy attacks.

Shushtar has been recognized as a UNESCO World Heritage site since 2009 due to its outstanding universal value and the significance of its hydraulic system as a cultural heritage site. The city has several other notable historical sites, including the Shushtar Historical Bazaar, the Jameh Mosque of Shushtar, and the Falak-ol-Aflak Castle. The city is also famous for its handicrafts, such as carpets, silk fabrics, and traditional clothing.