The rivers were the decisive factor in the formation of states in this part of the Middle East; the Euphrates and Tigris produced conditions under which an ordered society could develop in southern Iraq as early as the middle of the fourth millennium B.C .; the same rivers set their stamp on the special form of culture that we can describe as characteristic of ancient Iraq, and assured a continuity in the structure of society that was not really broken until the irruptions of the Mongols in a .d . 1258. The Greeks
recognized the fundamental significance of the rivers in this country when they called it Mesopotamia, ‘the land between the rivers5.