The Tigris River is located in Asia, running southeast from Turkey to Iraq where it joins the Euphrates to form the Shatt-al-Arab delta. This in turn flows into the Persian Gulf and is part of a canal and irrigation system that has been around since as early as 2400 B.C.
According to Infoplease, in ancient times, the Tigris River was an important route for trade and transportation. Due to this, several great cities of Mesopotamia, such as Nineveh and Seleucia, formed on its banks. The Tigris is approximately 1,150 miles long and is navigable by shallow-draft vessels to Baghdad. Above that, rafts carry much of the present-day trade to Mosul.