ozymandias said:
More like 2800 BCE for the first Egyptian dynasty and Sumer's heyday (although the Akkadians were actually dominant in the fertile crescent at this time).
In 4500 BCE Egypt was still a Neolithic culture whereas the fertile crescent was part of a larger Chalcolithic cultural grouping. The turning point at this juncture was copper working; Bronze working didn't hit the scene until about 2000 BCE.
-Oz
Neolithic or chalcolithic technology is not a barrier to organized civilization, and a number of civilizations represented in the game never had a central, unified state (eg the Scandinavians were a collection of small kingdoms in the "Viking" era). So I always took Sumeria to mean the pre-Akkadian collection of city-states, but maybe also including the Akkadian Empire. Their heyday might have been alot later, but there was a Sumerian civilization around in 4500 BC, advanced enough to have developed complex mathematics, a calendar, organized agriculture, a priest class, urban centres, and a primitive type of writing. Qualifies as a civilization in my mind, and even if it's fairly amorphous and indistinct as a term, the usual one is "Sumeria", even if properly that only refers to a small part of Mesopotamian civilization of the time - because its specific as to the time frame whereas "Mesopotamian" could mean anything right up to present-day Iraq.
I have a huge problem with the Enkidu warrior UU though, seems like they didn't really do their research too well and just sort of made this one up. Alot of cultures' warriors worshipped some hero or another, there's nothing really exceptional about it. The Sumerian UU should be an axeman, or possibly maceman, since their greatest innovation on the battlefield was a socketed copper axe or mace head (as opposed to earlier heads which were simply bound on).
I can't see any overlap with the Babylonians, two completely different time frames and style of civilization, the Sumerian period of Gilgamesh etc was over a thousand years before Hammurabi. And alot happened in between. The Babylonians weren't even really Sumerians, they were Amorites.