People moved out of the foothills and onto the plains. This region became known as Sumer
They built levees along the sides of the river to prevent flooding. When the land was dry, the farmers poked holes in the levees, allowing the water to flow through the holes and into the thirsty fields
The water was gross with silt. They had to work to gather to clean it. They created a big city.
These independent city-states often fought with one another. To defend themselves, the Sumerians built walls and dug moats around their cities.
I think that we are thanking of mare things to create.