Sumerians were polytheistic, which meant they believed in many gods. They built atop, large, stepped towers called ziggurats, which were the most important buildings in the civilization. Temples, priests and priestesses held a great deal of power, and kings were believed to derive their power from deities , making the government a theocracy. Human beings in general were considered inferior and were obliged to serve and obey gods.
As they grew, they gained power over the surrounding countryside, becoming city-states. Since Mesopotamia was located between two rivers , they had too little stone for building, so they had mud bricks.