Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Tigris-Euphrates river system is part of the Tigris-Euphrates alluvial salt marsh ecoregion of West Asia, and 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 part of the larger Fertile Crescent, it saw the earliest emergence of literate urban civilization in the Uruk period, for which reason it is often dubbed the Cradle of Civilization"."