In Aztec mythology, Tonatiuh (Nahuatl: Ollin Tonatiuh "Movement of the Sun") was the sun go. The Aztec people considered him the leader of Tollan, heaven. He was also known as the fifth sun, because the Aztecs believed that he was the sun that took over when the fourth sun was expelled from the sky. According to their cosmology, each sun was a god with its own cosmic era. According to the Aztecs, they were still in Tonatiuh's era. According to the Aztec creation myth, the god demanded human sacrifice as tribute and without it would refuse to move through the sky. It is said that 20,000 people were sacrificed each year to Tonatiuh and other gods, though this number is thought to be inflated either by the Aztecs, who wanted to inspire fear in their enemies, or the Spaniards, who wanted to vilify the Aztecs. The Aztecs were fascinated by the sun and carefully observed it, and had a solar calendar second only in accuracy to the Mayans'. Many of today's remaining Aztec monuments have structures aligned with the sun.