Mesopotamia is a word of Greek origin that means “between the rivers.” It lay between the Tigris and Euphrates Rivers, in what is now Iran and Iraq. The very first civilizations known to man emerged and flourished in this part of the world. The kingdoms of Akkad, Ur, Isin, Babylon, and Assyria supplanted each other in controlling most of the area from the third through the first millennia, B.C.E. They were succeeded by the Achaemenid, Parthian, and Sassanian Dynasties of ancient Persia.
Tracing the timelines of these peoples is not an exact science. The early rulers of Mesopotamia were powerful kings of separate city-states. At times a king of one city might control several other cities as well, thus dominating the area between the Tigris and the Euphrates. Several kings could be powerful at the same time, and so the timelines often overlap with each other.