Tigris and Euphrates are rivers that flow parallels and Sumer civilization was settle in southern part of Mesopotamia between them.
The Sumerians were organized in 12 main walled cities, each one with its own king until The Great Flood around 2800 BCE. The community life was divided in classes. All community worked together in cooperation and specializaded labour.
The highest position was priest-king which assumed a religious and political role; then there were the priests, whom was responsible for the rituals and services in the temples; then the administrative roles of the high officials and scribes; then landlords, shopkeepers and artisans and lastly, the slaves.
Due to the Flood the Sumerians developed a system of irrigation, that drained the rivers avoiding the flood, they dug canals and the water was stored and also used in the agriculture. In summer time they need to channel the water from the river distributing it to the lands farms. The irrigation system is still used today and the Sumerians also did the Cuneiform Script, which is the first written human system using words instead of signs. It had around thousand characters, which was reduced to six hundred and three millenniums later was replaced in the Roman Era for some kind of alphabet.
