Mesopotamia was the site of one of the earliest known civilizations. This fertile region, which lies between the Tigris and Euphrates rivers, includes a territory nearly 660 miles in length and 250 miles in width. The Sumerian civilization, with its capital city of Sumer, is believed to be the first civilization that originated here.
After the flood, the Tigris and Euphrates rivers most likely didn't follow the same path since the silt from the global flood changed the landscape of the entire Earth.