The ancient name for southern Mesopotamia (earlier called Sumer), which first became a political entity when an Amorite dynasty united Sumer and Akkad in the first half of the 2nd millennium bc. At this period its power extended over Assyria and part of Syria. After c.1530 bc first the Hittites then other invaders, the Kassites, dominated the land, and it became part of the Assyrian empire. With the latter’s decline Babylonia again became prominent under the Chaldeans (625–538 bc), only to fall to Cyrus the Great, whose entry into Babylon ended its power for ever.