Final answer:
Ziggurats are a key characteristic of the early Sumerian period of Mesopotamian culture, serving as places of worship for religious officials.
Step-by-step explanation:
Ziggurats are a key characteristic of the early Sumerian period of Mesopotamian culture. They were massive structures resembling terraced step pyramids, with a shrine or temple at the top. Ziggurats were built by stacking and piling sun-baked bricks, and they served as places of worship for religious officials. The first surviving ziggurats date to the Sumerian culture in the fourth millennium BCE.