The Tigris is the eastern member of the two great rivers that define Mesopotamia, along with the Euphrates, which flows from the mountains of Turkey through Iraq. Etymology The original Sumerian name was Idigna or Idigina, probably from *id (i)gina "running water", which can be interpreted as "the swift river", contrasted to its neighbor, the Euphrates, whose leisurely pace caused it to deposit more silt and build up a higher bed than the Tigris. This form was borrowed and gave rise to Akkadi… (More on Tigris)