Conversation so far:
which civilizations developed in the fertile valley between the tigris and euphrates rivers
Sumer is the earliest known civilization in ancient Mesopotamia, in the fertile valley between the tigris and Euphrates rivers, considered possibly the first human civilization anywhere in the world.
When was the origin of the Sumerian civilization
The origins of Sumer civilization are debated, but archaeologists suggest Sumerians had established roughly a dozen city-states by the fourth millennium B.C.

Question: What is known about the civilization
Self-contained rewrite: What is known about the Sumer civilization