What is the socio-economic structure of Sumerian society?

Sumerian civilization in present-day Iraq was one of the first societies in the world to create a social class system.  At the top of the social hierarchy was the ruling family.  Each city-state had a king and an aristocratic class that consisted primarily of the royal family.  Also highly regarded in Sumerian city-states were the priests that were responsible for keeping the gods happy.  They were in the upper classes and close in importance to the royal family.  A middle class emerged that consisted of warriors, scribes, merchants, and artisans.  Trade was very important in Mesopotamia and merchants could acquire wealth through trading with other city-states.  They had to work very hard for this wealth.

The lower classes in Mesopotamia consisted of farmers.  While they were very important to the city-states, they were not highly regarded.  A penal slave class existed below the farmers on the social hierarchy.