*Sumerian Civilization*
The Sumerian civilization is the oldest and first known civilization in Mesopotamia. This civilization can be identified from the 5th millennium BC.
It was these people who first created city-states, city-states that promised the first form of political system. This city-state was governed by a priest-king and derived its existence from a central temple that was governed by a precise agricultural system and trade with other city-states. In this city-state, a precise economic and religious order was established under the shadow of the priest-king.
The language of this people is a single family and is not related to any of the ethnic groups living in Mesopotamia. For this reason, the origin of this civilization has not been determined yet, but the formation of this civilization was the main structure of culture, religion, architecture, mathematics, astronomy, medicine and many other sciences in Mesopotamia, and after that other ethnic groups throughout Mesopotamia followed them.
The Sumerians are among the inventors of the world's first writing system (cuneiform). And it was thanks to this script that the first recorded myths, including the Epic of Gilgamesh, have come down to us. In astronomy, they were the ones who created the lunar and solar calendars based on the movement of the sun and moon, and in medicine, they distinguished and named diseases according to their symptoms (separating medicine from magic). 
Sumerian gods and religious customs, such as cuneiform and its epic literature, were widespread throughout Mesopotamia even after their collapse, and their language continued to survive as a temple and spiritual language.