Tigris–Euphrates river system through the central plain and combine at Al-Qurnah to form the Shatt al-Arab and discharge into the Persian Gulf. The region has historical importance as part of the Fertile Crescent region, in which civilization is believed to have first emerged. The ecoregion is characterized by two large rivers, the Tigris and Euphrates. The rivers have several small tributaries which feed into the system from shallow freshwater lakes, swamps, and marshes, all surrounded by desert. The hydrology of these vast marshes is extremely important to the ecology of the entire upper Persian Gulf. Historically, the area is known as Mesopotamia. As
Khabur (Euphrates) it the "Aborrhas" (Ἀβόρρας), and Isidore of Charax called it the "Aburas" (Ἀβούρας). It was described as a large river of Mesopotamia which rose in Mons Masius, about from Nisibis, and flowed into the Euphrates at Circesium (Kerkesiah). Procopius speaks of it as a river of importance, and Ammianus states that Julian the Apostate crossed it “per navalem Aborae pontem.” Strabo describes it as near the town of Anthemusia. The river is fed by several smaller streams, the names of which are mentioned in the later classical writers. These are, the Scirtus (Procop. "de Aedif." 2.7), the Cordes (Procop. "de