Teotihuacan, located just outside Mexico City, is the ultimate celestial city, though the names of its builders are no longer known. The Aztecs discovered the city as ruins, and built it into an empire. At Teotihuacan’s height, between the first and fifth centuries, 125,000 people lived in the city, which was larger than the walled city of Rome. The Sun Pyramid, at Teotihuacan’s center, is one of the largest structures of the ancient world — bigger than Giza!

Featured archaeologists describe the human activity and sun ceremonies conducted by the Aztecs, who created their calendar around the different positions of the sun at different times of the year. The structure of the cities and their relationship with Aztec religious beliefs are based on this cosmic calendar.