- Together with the Tigris, the most important river that defined the borders of Mesopotamia. The Euphrates has its source in the mountains of Anatolia, which receive substantial amounts of snowfall in the winter. The river was called purattu in Akkadian, a name that survives in the Arabic form Firat. Its main tributaries are the Balikh and the Habur. Farther south, as the alluvial plains begin and the gradient of the land becomes very low, the Euphrates carved out a number of subsidiary beds and side arms. It was an important means of communication by boat and less turbulent than the Tigris. While the upper reaches of the Euphrates were situated in the Fertile Crescent, where rain-fed agriculture was possible, south of present-day Baghdad began the dry zone. The Euphrates was one of the main sources of water that was channeled into numerous manmade canals. While most Mesopotamian cities were situated on side arms of canals, some, including Nippur and Babylon, lay directly along the main course of the river. Because of the low gradient of the plains and the soft soil, the river was liable to change course, sometimes drastically, and nowadays neither city lies in the vicinity of the stream.
Historical Dictionary of Mesopotamia. EdwART. 2012.