Ancient Maya Structures Were Aligned To A Mysterious 260-Day Calendar

This is evidence that Mesoamerican cultures used the 260-day calendar centuries earlier than previously known.

Ancient Mesoamerican cultures were using complex 260-day calendars based on knowledge of the solar system far earlier than previously realized. Understanding how these early cultures kept track of time has proved tricky due to the lack of written sources from the time, but researchers discovered the use of this advanced calendar system by looking at the astronomical orientations of hundreds of ceremonial structures. 

In a new study, archaeologists looked at data from aerial laser LiDAR scanning that was able to peer through the dense overgrowth of Central America to reveal the presence of long-lost structures. Among the 33,935 architectural complexes they sifted through, 478 were ceremonial complexes that belonged to the ancient Olmec and Maya civilizations between 1100 BCE to 250 CE.

This was a time when Mesoamerican civilizations were in their childhood. People were starting to shift from a constantly on-the-go hunter-gatherer lifestyle to a more sedentary settled style of living fuelled by maize agriculture.

The complexes were often rectangular in shape, featuring a flat plaza surrounded by rows of mounds, elongated structures, and pyramids. Like many of the Mesoamerican structures of this time, the buildings were carefully constructed to align with the Sun, Moon, and even the planets of our solar system. 

One of these sites in the research is Aguada Fénix, the largest building in the entire pre-hispanic history of the Maya area that’s believed to have been used as an astronomical viewing platform.

Amazingly, this new research shows that many of the structures are oriented in line with the solstices, quarter days, or lunar cycles in the 260-day year. For instance, a number of the structures are positioned in a way that corresponds with the sunrises on February 11 and October 29, separated by 260 days.

The site of Buenavista on the day of sunrise alignment. Image credit: Takeshi Inomata

These findings represent the first clear evidence that the Maya possessed sophisticated knowledge of the stars dating back to at least 1100 BCE. It’s also the earliest known evidence of the 260-day calendar.

In the 260-day cycle, 20 day names run from one to 13, totaling a cycle of 260 days. It is a calendar system that’s believed to be unique to the Mesoamerican culture. 

No one is certain why they used this number of days in a cycle, but theories range from some kind of numerological significance, agricultural scheduling, or even the human gestation period (since 260 days is almost 9 months). 

“For the Maya and other Mesoamerican groups, numbers 20 and 13, associated with human body parts, particular deities, and cosmic levels, were particularly important. Although our data are not enough to resolve the origin of the 260-day calendar, they lead us to favor two alternative scenarios, each combining the numerology and the scheduling of rituals,” the study authors write. 

Both of these scenarios involve agriculture and the seasons and would require some fairly advanced knowledge of the solar system's cycles. It’s notable that most of the structures are linked to dates in February and March, the height of the dry season. This was a period of the year when horticulturalists were freed from their work in cultivation fields and took part in activities like aggregation, collective ritual, and construction activity. 

Perhaps, the researchers suggest, the rise of the 260-day calendar has some kind of connection to the advent of agriculture and the cultures’ growing understanding of the celestial kingdom above us. 

 The new study was published in the journal Science Advances. 

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