The Sumerian civilization arose around 4500-4000 BC in the fertile crescent region between the Tigris and Euphrates Rivers in Mesopotamia. Sumerian society was composed of independent city-states like Ur and Kish that were ruled by kings with both governmental and religious powers, forming a theocratic system. Farming was central to their economy and they developed innovations like the wheel, lunar calendar, and a base-60 number system. Religion was important in Sumerian culture and each city had its own patron deity housed in a ziggurat temple.