The ziggurats are the pyramids of Mesopotamia (modern day Iraq). In the past every ziggurat was topped by a temple. Being the closest thing to heaven, it became the place where priests contacted the gods.The ziggurat shown is from the ancient city of Ur and is dramatic in size, being as high as a thirty storied building.
The top of the ziggurats were also ideal for astronomical observations, since it gave an unobstructed view of heavens. The priest believed that the positions of
the heavenly bodies contained information about the will of the gods and the study of the night sky therefore became one of their most important tasks. These priests, therefore, were rightly believed to be the first professional astronomers. They discovered all the planets visible to the naked eye.
"The Great World History Book"