Mesopotamia, located between the Tigris and Euphrates Rivers (modern day Iraq), was one of the earliest cradles of civilization beginning around 4000 BCE. The Sumerians, who lived in southern Mesopotamia, developed one of the first complex societies by establishing cities, a system of governance, and new advances like irrigation, writing, and wheeled vehicles. They also had polytheistic religions where gods controlled nature and humans were believed to have been created from river mud. While early Mesopotamian civilization achieved many cultural and technological firsts, women had very few rights under male-dominated social structures.