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.
What is known about the Sumer civilization
Ancient Sumerians were among the first to use bronze. They pioneered the use of levees and canals for irrigation. Sumerians invented cuneiform script, one of the earliest forms of writing.
What are some archeological sites in the Fertile valley of the Mesopotanian region built by Sumerians
Some of the most famous Mesopotamian archaeological sites in the fertile Valley include: Ziggurat of Ur, Babylon, Hattusha, Persepolis.

Question: What countries does the region cover
Self-contained rewrite: What countries does the fertile Valley between tigris and Euphrates cover