The Mayan Empire flourished from around 250 AD to 900 AD in Mesoamerica. They developed accurate calendars and advanced knowledge of astronomy, mathematics, and engineering. The Mayans were polytheistic and based their religion and calendars around their nature gods. They built temples and made human sacrifices to the gods. While the reasons for the decline of the Mayan civilization are uncertain, their detailed calendars notably included predictions about the end of the current world age in 2012.