Ancient Zapotec inscriptions carved at Monte Albán in southern Mexico may contain the oldest known record of a lunar calendar in the Americas, according to new research that sheds light on how one of Mesoamerica’s earliest civilizations tracked time more than 2,000 years ago.
The study, published in Latin American Antiquity, found that a recurring symbol in Zapotec inscriptions recorded the number of days since the first visible crescent moon after a new moon. The discovery pushes evidence for lunar day counts back to at least the fifth century BCE, centuries earlier than previously documented examples elsewhere in Mesoamerica.
Researchers led by John Justeson analyzed inscriptions from Monte Albán, the ancient Zapotec capital in present-day Oaxaca. They focused on a symbol known as “Glyph W,” which appears alongside dates recorded in the region’s complex calendrical system.
Searching for the meaning of Glyph W
For decades, scholars debated the meaning of Glyph W. Some suggested it marked a day within a month or identified a position within a ceremonial calendar. However, none of those explanations consistently matched the inscriptions.
The new study argues that the symbol instead recorded a lunar day count. In practical terms, it indicated how many evenings had passed since the first appearance of the moon’s crescent following a new moon.
Researchers examined seven well-preserved inscriptions that contained both Glyph W and dates tied to the Mesoamerican 52-year calendar cycle. By comparing the intervals between these recorded events and matching them with known lunar cycles, they identified a pattern that closely aligns with the moon’s average 29.5-day cycle.
Evidence of a lunar day count
The analysis revealed that the recorded dates could fit seven possible placements in absolute time between about 650 BCE and 50 BCE. Only one of those placements also matched features of the Zapotec calendar documented centuries later during the colonial period. That chronology places the inscriptions between roughly 496 BCE and 221 BCE.
The findings suggest that Zapotec astronomers carefully monitored the moon and incorporated those observations into their written records. Researchers say the system resembles later Maya lunar counts, which became widespread many centuries afterward.
How the Zapotec tracked time
The discovery is significant because Monte Albán preserves the earliest large body of hieroglyphic writing known from Mesoamerica. The inscriptions provide a rare glimpse into how early societies organized time, recorded historical events and connected celestial observations to religious and political life.
Researchers also found evidence that the Zapotec divinatory calendar likely changed dates around midday rather than at midnight. Historical records from the 16th century describe a similar practice among Zapotec communities.
According to the study, one inscription appears to document a ceremony linked to the return of a “year-bearer,” a special calendar date associated with the beginning of the year. Researchers concluded that the event was probably celebrated in the afternoon by at least 222 BCE.
Clues from the moon’s first appearance
The study relied on a combination of epigraphy, archaeology, linguistics and astronomy. Researchers reconstructed ancient lunar visibility at Monte Albán by modeling when the moon’s crescent would first have been visible from the site’s elevated position overlooking the Oaxaca Valley.
They then compared those observations with the dates recorded in the inscriptions. Thousands of possible chronological combinations were tested before researchers narrowed the results to a handful of viable solutions.
Rewriting the history of Mesoamerican astronomy
The work also challenges earlier interpretations of Glyph W that had remained influential for decades. Researchers found that previous theories failed to explain several complete inscriptions and produced inconsistencies when compared with known calendar patterns.
Beyond solving the mystery of a single symbol, the findings provide new evidence that sophisticated astronomical observation was already embedded in Zapotec society during the first millennium BCE.
Researchers say the inscriptions demonstrate that lunar day counts were used in Mesoamerica about 857 years earlier than previously known. The discovery highlights the scientific and intellectual achievements of the Zapotec civilization and offers a deeper understanding of how ancient peoples observed the sky and organized their world around celestial cycles.
See all the latest news from Greece and the world at Greekreporter.com. Contact our newsroom to report an update or send your story, photos and videos. Follow GR on Google News and subscribe here to our daily email!
