While the Sumerians were still engaged in their heydey, the Assyrians were settling in further up the Tigris river. Chief among their cities were Assur and Nineveh. At various times they were held as part of the various Sumerian empires. Later Babylonia conquered and held Assyria as a vassal state. It was somewhere around 1100 BCE that the fortunes of Babylonian and Assyrian were changed by the conquest of Babylon by Assyria under the leadership Tiglath Pileser I. But their hold on Babylonia was never all that strong, and control over the region kept shifting between the two powers.