The Shatt al-Arab (, "River of the Arabs"), also known as Arvand Rud in Iran (, "Swift River"), is a river of some 200 km (120 mi) in length formed by the confluence of the Euphrates and the Tigris in the town of al-Qurnah in the Basra Governorate of southern Iraq. The southern end of the river constitutes the border between Iraq and Iran down to the mouth of the river as it discharges into the Persian Gulf. It varies in width from about at Basra to at its mouth. It is thought that the waterway formed relatively recently in geologic time, with the Tigris and Euphrates originally emptying into the Persian Gulf via a channel further to the west.