The Ubaid Period (c. 5000-4100 BCE) when the so-called Ubaid people first inhabited the region of Sumer is followed by the Uruk Period (4100-2900 BCE) during which time cities began to develop across Mesopotamia and Uruk became the most influential. The Uruk Period is divided into 8 phases from the oldest, through its prominence, and into its decline based upon the levels of the ruins excavated and the history which the artifacts found there reveal. The city was most influential between 4100-c.3000 BCE when Uruk was the largest urban center and the hub of trade and administration. In precisely what manner Uruk ruled the region, why and how it became the first city in the world, and in what manner it exercised its authority is not fully known. The historian Gwendolyn Leick writes, “The Uruk phenomenon is still much debated, as to what extent Uruk exercised political control over the large area covered by the Uruk artifacts, whether this relied on the use of force, and which institutions were in charge. Too little of the site has been excavated to provide any firm answers to these questions. However, it is clear that, at this time, the urbanization process was set in motion, concentrated at Uruk itself” (183-184). Since the city of Ur had a more advantageous placement for trade, further south toward the Persian Gulf, it would seem to make sense that city, rather than Uruk, would have wielded more influence but this is not the case.