It is thought that Sumerian society really started to take shape, though, between 4000 B.C. and 3100 B.C. This time is known as the Uruk period, and it saw the land becoming more urbanized. Indeed, towards the end of this era, Sumer had split into multiple city-states.
Canals were constructed and boundaries were raised to distinguish between these city-states. Furthermore, each of these places had a patron deity whom the population would worship in a particular temple built in their honor. And, at the same time, kings or governors known respectively as lugals and ensis ran the cities.
Now although some believe the earliest cities emerged in India or China, it is actually widely held that the Sumerian cities were the first. Eridu is reckoned to be the oldest of these, and it can still be seen today as ruins. Meanwhile, about seven-and-a-half miles away from Eridu lies evidence of the city of Ur.