The Land. Mesopotamia in Greek means the "land between the rivers," in this case the rivers Tigris and Euphrates. In its broadest sense, however, Mesopotamia encompassed not only the land between these two rivers, but the lands (occasionally for hundreds of kilometers) on both sides of their banks and of their major tributaries. Throughout prehistory and history, this vast area was occupied by a wide range of ethnic and linguistic groups. Thus, it becomes both convenient and necessary to distinguish specific areas in specific periods of time. In the third millennium B.C.E., on the alluvial plain—a broad flat land covered by thick layers of sediment deposited by the flooding rivers—between the marshlands at the head of the Persian Gulf north to the area of modern Baghdad were the lands of Sumer, to the south, and Akkad, to the...