Maya calendar may be more than 3000 years old, laser mapping reveals

In the western, volcano-ringed highlands of Guatemala, Willy Barreno Minera keeps watch over the skies. As an ajq’ij , a daykeeper and spiritual guide, the stars and landscape help him keep track of the 260-day calendar that has ruled the life of his Maya K’iche’ community—an Indigenous group of about 1.6 million people—in Quetzaltenango for generations. Exactly how long people have been using this timekeeping system has posed a mystery. But a new study suggests the ancient calendar used by Maya and Olmec cultures may date back as early as 1100 B.C.E., centuries earlier than previous estimates.

“We know that it’s very old,” says David Stuart, an epigrapher at the University of Texas, Austin, who was not involved in the new study. “We just didn’t have any direct evidence for it.”

The 260-day calendar, or cholq’ij (order of the days), has only been found in the Maya region of Mexico and Central America. Timekeepers notated the passage of time using combinations of 13 numbers and 20 symbols, always in the same sequence. (For instance, 6 January 2023, would be “6 Rabbit” according to the cholq’ij .) We now know the calendar days correspond to alignments between the stars, architectural features of buildings, and natural landmarks.

This unique time span may have helped the culture guide decisions related to agriculture, religion, politics, and more. (The Maya also used another calendar, known as the haab , that consists of 365 days and corresponds with the solar cycle.)

Before the new study, the earliest evidence of this calendar came from a mural containing a piece of hieroglyphic script found in San Bartolo, Guatemala, dated to 300 B.C.E. Such written records offer a spotty account of the region’s history, though, Stuart says, because the Maya frequently used perishable materials that have been lost to time.

Hoping to find more permanent evidence, Ivan Šprajc, an archaeologist at the Institute of Anthropological and Spatial Studies in Slovenia, turned to a laser-mapping technique known as lidar that can reveal ancient structures—and their cosmic alignments—hidden under dense growth.

Two years ago, archaeologist Takeshi Inomata of the University of Arizona published the largest lidar survey to date of the lowlands of Mexico’s Gulf Coast, revealing almost 500 ancient monuments , most of them unexplored. Intrigued, Šprajc began a collaboration with Inomata to analyze 415 of those complexes to see how they aligned with the rising and setting of the Sun, the Moon, Venus, and other celestial bodies.

The team found that most of the complexes showed an east-west alignment, and almost 90% of them featured architectural points that aligned with sunrises on specific dates. Most commonly, these sunrises fell on 11 February and 29 October of the Gregorian calendar , which have 260 days in between them , the researchers report today in Science Advances . The earliest of these complexes date to about 1100 B.C.E., in an era known as the Formative period, suggesting the 260-day calendar is at least that old.

Other monuments pointed to sunrises had 130-day—half a calendar—intervals. And yet other monuments’ alignments matched sunrises separated by multiples of 13 or 20 days, reflecting the calendar notation system’s 13 numbers and 20 signs and corresponding to equinoxes and solstices. The orientation of some complexes also matched Venus and Moon cycles, which are associated with the rainy season and maize growing. Other complexes didn’t appear to have a specific orientation, which sparks more questions about other possible cosmological alignments, Šprajc says.

“What’s fascinating to me,” Stuart says, “is that there is this regularity and consistent pattern … from the very beginning and they last for centuries throughout the history of Maya architecture.”

The new results present “good, tight evidence that the Mayan calendar had its origins way back before we have the actual written evidence for it,” he adds. “To see it architecturally is fantastic.”

A strength of the new study lies in its large sample size spanning so many years, adds Gabrielle Vail, an archaeologist and epigrapher at the University of North Carolina, Chapel Hill. The results appear to support other written evidence that timekeeping arose during the Formative period, she adds. “It’s very exciting to see. It really supports what a lot of us have thought for a number of years.”

The earliest structures the researchers studied date back to the time when groups were just starting to transition from a hunter-gatherer lifestyle to an agricultural one, Šprajc says. The cultivation of maize was just beginning to become more important, and the 260-day calendar might have also been useful to indicate when certain resources would be more plentiful, he says. Šprajc says he believes the cholq’ij is intimately tied to timing the growth cycle of maize, a staple of both ancient and modern-day Mesoamerican cultures, as well as to human pregnancy, which roughly lasts about 260 days.

In the present day, Barreno Minera still uses the cholq’ij to advise his community when to start preparing the soil to plant maize, around mid-February. His wife, Ixquik Poz Salanic, also a daykeeper and lawyer, uses both Moon cycles and the calendar to offer medicinal advice and help midwives with childbirth timing. And until relatively recently, their community also used the calendar to mark when it was time to change government administrations.

Barreno Minera says he has great admiration for the researchers who study his culture and ancestors, and are helping recover more knowledge about their ancient systems. But he also wishes the researchers of the new study had approached daykeepers like him, as well as farmers who still use the calendar to farm maize, to inform their work.

“Daykeeping is not close to being lost,” Barreno Minera says. “Even when we don’t have great Maya architecture anymore, we never lost count of the days. We say that when the [Spanish] colonizers came, they burnt the books, they destroyed the steles. But they did not burn the sky, they did not burn the Sun.”