Illustration of the Maya tzolkin, or sacred calendar

Date of origination: prior to 500 B.C.E.

No one knows for certain where the first Mesoamerican calendar systems arose, but two very likely places are the Olmec homeland, along the southern gulf coast of Mexico, and the Zapotec city of Monte Albán in Mexico's Oaxaca (pronounced wah-HAH-kah) Valley. Virtually every Mesoamerican civilization from the Olmecs forward used a calendar system that combined two calendars: the sacred 260-day calendar now known as the tzolkin and the practical 365-day solar calendar called the haab.