The Euphrates is the western of the two rivers that define the borders of Mesopotamia. The other is the Tigris, which joins the Euphrates to form the Shatt-al-Arab and flow into the Persian Gulf. Several dams have been built since the 1970s. As a result, less water flows down the river into the sea. The Euphrates, along with the Tigris, were very important to ancient Mesopotamians because they would provide water and irrigation. It is 1,728 miles long and is one of the longest rivers in all of Mesopotamia. It is slower than the Tigris river but at the same time longer.