bends southwest, bisecting the city of Ahvaz, and south through farmland to its mouth on the Arvand Roud at Khorramshahr, where its water, together with that of the Tigris and Euphrates, turns sharply southeast to flow to the Persian Gulf. Basin The largest river by discharge in Iran, the Karun River's watershed covers in parts of two Iranian provinces. The river is around long and has an average discharge of . The largest city on the river is Ahvaz, with over 1.3 million inhabitants. Other important cities include Shushtar, Khorramshahr (a port), Masjed-Soleyman, and Izeh. Much of Khuzestan's transport and resources are connected in one way or another to the Karun. Since the British first discovered oil at Masjed Soleyman, the Karun has been an important route for the transport of petroleum to the Persian Gulf, and remains an important commercial waterway. Water from the Karun provides irrigation to over of the surrounding plain and a further are planned to receive water. History Karun River lies between the Susa plain, the location of the ancient cultures dating back to the fifth millennium BC and, to the south, the newly discovered ancient culture of the Zohreh River plain from the same period. The principal ancient site being excavated near the Zohreh River is Tol-e Chega Sofla, which has many parallels with Susa. Sites along the Karun also participated in these historical developments. Later, the Karun valley was also inhabited by the Elamite civilization which rose about 2,700 BC. At several points in history, Mesopotamian civilizations such as Ur and Babylon overthrew the Elamites and gained control of the Karun and its surroundings in modern Khuzestan. However, the Elamite empire lasted until about 640 BC, when the Assyrians overran it. The city of Susa, near the modern city of Shush between the Dez and Karkheh rivers, was one of their largest before it was destroyed by the invaders. The first known major bridge across the river was built by the Roman captives that included its emperor Valerianus in the Sassanid era, whence the name of the bridge and dam Band-e Kaisar, "Caesar's dam", at Shushtar (3rd century AD). In two of several competing theories about the origins and location of the Garden of Eden, the Karun is presumed to be the Gihon River that is described in the Biblical book of Genesis. The strongest of these theories, propounded by archaeologist Juris Zarins,