The Olmec and Mayan peoples built star-aligned ceremonial centers to keep track of the important days of a 260-day calendar. These peoples are thought to have lived on the Gulf Coast of Mexico some 3,100 years ago.
The earliest written evidence of this calendar, found at a Maya site in Guatemala, dates to about a thousand years later, between 300 and 200 BC. However, scientists have long hypothesized that Gulf Coast Olmec groups devised a 260-day calendar hundreds of years ago.
Archaeologist Ivan Šprajc and colleagues say that light sensing and range determination, or aerial laser mapping called lidar, has revealed the astronomical orientations of 415 ceremonial complexes dated between 1100 BC and 250 AD.
According to the researchers’ findings published in the journal Science Advances, the majority of the ritual locations were arranged on an east-to-west axis that corresponded to dawn or other astronomical events on specific days of a 260-day year.
This discovery demonstrates the earliest proof of a structured calendar system in the Americas that incorporated astronomical knowledge and earth architecture. This system used celestial events to determine important dates during a 260-day part of the year.
“The oldest Mayan calendar”
Šprajc, from the Research Center of the Slovenian Academy of Sciences and Arts, said: “The 260-day cycle is embodied in Mesoamerica’s oldest known monumental complexes and is used to plan seasonal, livelihood ceremonies. We can’t be sure exactly when or where it was invented.”
Some of the earliest ceremonial centers identified with lidar clearly belong to the Olmec culture, but others are difficult to classify, says Stephen Houston, a Brown University archaeologist who was not involved in the new study.
Olmec society dates back about 3,500 to 2,400 years. The links between the Olmec and later Maya culture, known for their Classical-era cities and kingdoms that flourished about 1750 to 1100 years ago, are unclear. However, Classic Maya inscriptions and documents also refer to the 260-day calendar.
Šprajc and colleagues suggest that traveling groups in Mesoamerica, an ancient cultural region stretching from Central Mexico to Central America, may have planned large, seasonal gatherings using the 260-day calendar long before it gained popularity among Classic Maya kings.
They add that the same calendar may have marked days of important agricultural activities or rituals as maize cultivation became widespread in Mesoamerica, beginning around 3,000 years ago. Some Mayan communities still use a 260-day calendar to regulate the planting of maize and plan agricultural rituals.
“Maya city comparison with previous data”
Previous lidar data had shown that ceremonial centers based on a common plan emerged in many Olmec and Maya sites along Mexico’s Gulf Coast about 3,400 years ago. The calendrical significance of the alignment of ceremonial centers was only now revealed.
The most common architectural alignment detected in the new study corresponded to the position of sunrises 260 days apart on February 11 and October 29, when the complexes were in use. These complexes were facing east towards a point on the horizon where the sun rose on those two days.
Another common alignment was matching the sunrise 130 days apart, or halfway through the 260-day count.
Few of the ceremonial complexes were aligned with the solstices (the longest and shortest days of the year), the quarter days (the midpoint of each half of the year), or the lunar cycles in the 260-day year. The location of Venus, a star connected to the wet season and corn production, was followed by other centers.
At ceremonial centers, sunrises and sunsets were frequently separated by multiples of 13 or 20 days. According to Prajc, the numbers 13 and 20 also stand for the fundamental mathematical units of a 260-day year and have long been connected to a variety of deities and holy ideas among the Maya and other Mesoamerican communities.
Houston says future excavations at lidar-identified ceremonial complexes could explore whether ancient groups formally dedicated specific structures to specific days of the 260-day year.
Article : Šprajc, I., Inomata, T., & Aveni, A. F. (2023). Origins of Mesoamerican astronomy and calendar: Evidence from the Olmec and Maya regions. Science Advances, 9(1).