Mesoamerican Calendar

The Mesoamerican Calendar is what modern archaeologists call the method of tracking time used—with some variations—by most of ancient Latin America, including the Aztecs, Zapotecs, and Maya. In fact, all of the Mesoamerican societies were using some form of the calendar when the Spanish conquistador Hernan Cortes arrived in 1519 CE.

History

The mechanisms of this shared calendar involved two parts that worked together to make a 52-year cycle, known as the Sacred and Solar rounds, such that each day had a unique name. The Sacred cycle lasted 260 days, and the Solar one 365 days. The two parts together were used to keep chronologies and king lists, mark historical events, date legends, and define the beginning of the world. The dates were chiseled into stone steles to mark events, painted on tomb walls, carved onto stone sarcophagi and written into bark cloth paper books called codices.

The oldest form of the calendar—the solar round—was likely invented by the Olmec, epi-Olmec, or Izapans about 900-700 BCE, when agricultural was first established. The sacred round may have been developed as a subdivision of the 365-year one, as a tool specifically designed to track important dates for farming. The earliest confirmed combination of sacred and solar rounds is found in the Oaxaca valley at the Zapotec capital site of Monte Alban. There, Stela 12 has a date which reads 594 BCE. There were at least sixty or so different calendars invented in pre-Columbian Mesoamerican, and several dozen communities throughout the region still use versions of it.

The Sacred Round

The 260-day calendar is called the Sacred Round, the Ritual Calendar or the Sacred Almanac; tonalpohualli in the Aztec language, haab in Maya, and piye to the Zapotecs. Each day in this cycle was named using a number from one to 13, matched with 20-day names in each month. The day names varied from society to society. Scholars have been divided about whether the 260-day cycle represents the human gestation period, some as-yet unidentified astronomical cycle, or the combination of sacred numbers of 13 (the number of levels in heaven according to Mesoamerican religions) and 20 (Mesoamericans used a base 20 counting system).

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However, there is growing evidence to believe that the fixed 260 days running from February to October represents the agricultural cycle, keyed to the trajectory of Venus, combined with observations of the Pleiades and eclipse events and potentially appearance and disappearance of Orion. These events were observed for more than a century before being codified in the Maya version of the almanac during the second half of the fifteenth century CE.

Aztec Calendar Stone

The most famous representation of the sacred round is the Aztec Calendar Stone. The twenty-day names are illustrated as pictures around the outside ring.

Each day in the sacred round had a particular fate, and, as in most forms of astrology, an individual's fortune could be determined on the basis of her birth date. Wars, marriages, planting crops, all were planned based on the most propitious days. The constellation Orion is significant, in that around 500 BCE, it disappeared from the sky from April 23 to June 12, its annual disappearance coinciding with the first planting of maize, its reappearance when the maize was sprouting.

The Solar Round

The 365-day solar round, the other half of the Mesoamerican calendar, was also known as the Solar calendar, tun to the Maya, xiuitl to the Aztec, and yza to the Zapotec. It was based on 18 named months, each 20 days long, with a five day period to make a total 365. The Maya, among others, thought those five days were unlucky.

Of course, today we know that the earth's rotation is 365 days, 5 hours and 48 minutes, not 365 days, so a 365 day calendar throws an error of a day every four years or so. The first human civilization to figure out how to correct that was the Ptolemies in 238 BC, who in the Decree of Canopus required that an extra day be added to the calendar every four years; such a correction was not used by the Mesoamerican societies. The earliest representation of the 365-day calendar dates about 400 BCE.

Combining and Creating a Calendar

Combining the Solar Round and Sacred Round calendars provides a unique name for each day in a block of every 52 years or 18,980 days. Each day in a 52-year cycle has both have a day name and number from the sacred calendar, and a month name and number from the solar calendar. The combined calendar was called tzoltin by the Maya, eedzina by the Mixtec and xiuhmolpilli by the Aztec. The end of the 52-year-cycle was a time of great foreboding that the world would end, just as the end of modern centuries are celebrated in the same way.

Archaeologists believe that the calendar was constructed from astronomical data built from observations of the movements of the evening star Venus and solar eclipses. Evidence for this is found in the Madrid codez( Troano codex), a Maya screen-fold book from Yucatan that most likely dates to the second half of the 15th century CE. On pages 12b-18b can be found a series of astronomical events in the context of the 260-day agricultural round, recording solar eclipses, the Venus cycle, and solstices.

Formal astronomical observatories are known in several locations throughout Mesoamerica, such as Building J at Monte Alban; and archaeologists believe that the Maya E-Group is a patterned temple type that was used for astronomical observation as well.

The Maya Long Count added another wrinkle to the Mesoamerican calendar, but that's another story.

Sources

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