Sumer was an ancient civilization of southern Mesopotamia which existed from 4500 to 1900 BC. It was first settled between 5500 BC and 4000 BC by the Ubaidians, as the Persian Gulf included large parts of southern Iraq at the time. The Ubaidians drained the marshes for agriculture, developed trade, and established industries such as weaving, leatherwork, metalwork, masonry, and pottery. In the first half of the third millennium BC, the first cities emerged in Mesopotamia, and the Sumerians established their own city-states including Kish, Uruk, Ur, Lagash, and Umma. Around 2270 BC, Akkad conquered Sumer, beginning a cycle of unifying empires being conquered by larger ones, which would then be conquered by larger ones, and so forth.