The Mesopotamian River Valley Civilization developed an intricate social system that was enforced by religion and partly economics. At the top of this system were the ruling elites of individual city-states. They maintained their position at the top of the class system because they were believed to have a been sent by the gods to govern. Religion was very important in Mesopotamia, so the authority of the ruling elites was never questioned. People didn't not want to rebel against the kings because they didn't want to risk relogious punishment. Just below the kings were the priests. These priests performed religious rituals and intervened with the gods. Because they possessed religious status, people feared religious consequence and obeyed them. Beneath the priests were the free commoners. Free commoners had no religious status and therefore were not obeyed by the upper class. Free commoners were usually builders, artisans, physicians, or engineers. After the free commoners were the dependent clients. Dependent clients did not own property and worked on others' estates to pay off any debt that they owed. They, like the free commoners, had no religious influence, but they had less financial status so they possessed less power than the free commoners. At the very bottom of the class system were the slaves. Slaves were usually prisoners of war, criminals, or debtors (people in substantial amounts of debt sold themselves into slavery to pay off their debt). They possessed no religious influence and no financial staus and had almost no freedoms.