This is the oldest known use of the Maya calendar
It was almost destroyed by a construction project 2,200 years ago.
KIONA N. SMITH - 4/15/2022, 10:07 AM
An artist's sketch of what the 300-200 BCE temple complex at San Bartolo looked like in its heyday.
Stuart et al. 2022
Amid rubble buried beneath a Maya pyramid in Northern Guatemala, archaeologists found a broken bit of plaster with a glyph painted on it. A bar-and-dot symbol for the number 7 is drawn above a deer head, representing 7 Deer, a date in the 260-day Maya calendar system. At around 2,300 years old, the painted plaster is the oldest known use of the calendar system once used by cultures across Mesoamerica, including the Aztec and the Mayaand still used by many Maya communities today.
Its persistence in many communities up to the present day stands as a testament of its importance in religious and social life, wrote University of Texas archaeologist David Stuart and his colleagues in their recent paper about the glyph. Our ability to trace its early use back some 23 centuries stands as another testament to its historical and cultural significance."
7 Deer, 2,300 years ago
The Maya calendar combines the numbers 1 through 13 with 20 words for animals, plants, or concepts. Those 20 words rotate in a set order; for instance, Deer is always followed by Rabbit, Water, Dog, Monkey, and Grass. When the numbers paired with the days reach 13, they start over, so 13 Rabbit would be followed by 1 Water, 2 Dog, and so on. (Pop quiz: Whats the day after 7 Deer?)
Eventually, that system produces 260 combinations of numbers and words. But heres where things get slightly complicated because a Maya year still lasted 365 days. The first day of the year could fall on any day whose name included a Year-Bearer, one of the animals, plants, or concepts allowed to start a new year. Think of it as similar to the way New Years Day can fall on any day of the week in our system; the year can start on a Tuesday or a Friday with no problem.
More:
https://arstechnica.com/science/2022/04/this-is-the-oldest-known-use-of-the-maya-calendar/