Sumer was one of the first ancient civilizations of Mesopotamia ("the land between the rivers [Tigris and Euphrates]), an area now covered by modern Iraq. Part of the development of Sumerian society was determined by the necessity of cooperation to irrigate the fertile agricultural land. Sumer began as a series of city states, dominated by a theocracy. The palace and Temple hierarchies were closely intertwined, and the King had authority in part authorized by the gods. Society was highly stratified, with nobles, craftsmen, serfs and slaves occupying distinct social roles and following their fathers in profession and class. Women had very limited rights and distinct domestic spheres of activity. Power was highly centralized, but the ideology of power stressed the rule of law.