The Tigris is the eastern member of the two great rivers that define Mesopotamia, the other being the Euphrates. In Greek, Mesopotamia means between two rivers. The river flows south from the mountains of southeastern Turkey through Iraq and empties itself into the Persian Gulf. The Ancient Greek form Tigris was borrowed from Old Persian Tigrā, itself from Elamite Tigra, itself from Sumerian Idigna. The original Sumerian Idigna or Idigina was probably from “running water”, which can be interpreted as “the swift river”, contrasted to its neighbor, the Euphrates. Another name for the Tigris used in Middle Persian was Arvand Rud, literally “swift river”. Today, however, Arvand Rud refers to the confluence of the Euphrates and Tigris rivers (known in Arabic as the Shatt al-Arab). In Kurdish and in southeastern Turkey the river is known as Dicle also known as Ava Mezin, “the Great Water”. Rising in the Taurus mountains of southern Turkey, the Tigris flows southeast through Iraq, where in the southern part of that country it merges with the Euphrates to become the Shatt al Arab, which then flows to the Persian Gulf. The river has numerous small tributaries running from its eastern bank, and is 1,180 miles (1,899 km) in length.