Across Mesoamerica, from Yucatan to Mazatlan, there was one general shape of the calendar shared by all the "higher" (i.e. urban) cultures the one world between the waters. This design apparently was in use as early as the Olmec "mother-cuture" period (2000 b.c.–100 b.c.).
Eventually there would be many versions of this one calendar system, and each culture and language would have their own names for the days and gods who rule those days, although in some cases the names represented the same animal, thing, or god.
The Mesoamerican calendar testifies to the genius and originality of the ancient American civilization. Their separate world had little or no contact with ancient Europe, Asia, or Africa — although there is some evidence of early contact in the shapes of giant Olmec statue heads, and in certain Asian or Chinese cultural similarities. Nevertheless the Mesoamericans developed a distinct calendric system markedly different than either the oriental or the Gregorian (which now rules the world).
Instead of seven days and twelve months, the Mesoamerican calendar revolves around 18 so-called "months" of 20 named days and thirteen, as well as 20, numbers.
It is customary among casual students such as ourselves, as well as the scholars whom we read, to focus on two general variations of the Mesoamerican calendar: the Aztec and the Maya. This emphasis is somewhat misleading (being over-simplified), although useful for illustrating the surface differences and underlying unity amongst Mesoamerican calendars.
One outstanding difference between the two was that the classic Maya (before 1000 a.d.) extensively used the "long count" to record their history on stone and in painting. In the long count (the name was invented by western archeologists), time was divided into 20 days, 18 "months", tuns (single years), katuns of 20 years, and baktuns of 400 years. While the Aztecs did not use the larger "long count" system, they did have the 20 days and 18 months (with their own names, of course).
It should be noted that a common feature of both Mesoamerican calendar and mathematics is the use of base 20, rather than 10. This is another factor completely different from the Europe-Africa-Arabic-Indo-Chinese "old world" cultural spectrum.
General form of the Mesoamerican calendar: 365/260 days
The chief traits shared amongst the various Mesoamerican calendars are:
the existence of a double calendar:
one calendar is 260 days long (a sacred, religious system)
and one is 360 plus 5 days long (a daily, normal calendar)
both systems (365/260) have twenty named days, and
the numbers one through thirteen, and one through 20 (or zero-12 and zero-19, or two-14, or other similar variations) are recounted over and over again.
The 365 day calendar is obviously bounded by the solar year, which is roughly 365.25 days long (leading to a Gregorian leap year of 366 days every fourth year). In our reading, we have discovered some variance of opinion among scholars as to whether the Mesoamericans practiced any such intercalery adjustments as leap year – there is some speculation that at times priest/astronomers gathered together to make adjustments, and that perhaps one such conclave was recorded in certain carvings on the "Temple of Quetzalcoatl" (modern name) in Xochicalco.
The 260 day sacred calendar, and the precise mathematical way it interacted with the 360+5 day solar calendar, seems unique to Mesoamerica. We have not heard of any other similar system anywhere else on Earth.
Both calendars were used at the same time, and continually measured out each other's numbers. Mathematically, the 260 and 365 day calendars coincide every 52 years. For the Aztecs, as presumably for the Toltecs before them (and perhaps also earlier Teotihuacan), this 52-year turning point was a time for special ritual and sacrifice. It was called the binding up of years.
The Maya, in contrast, even before they stopped using the long count around the year 1000 a.d., prefered to reckon time in bundles of 20 years (katuns), and did so (according to the Book of Chilam Balaam) even after the Spanish conquest.
With regard to the Aztecs, we westerners are accustomed to think of that 52-year time period as being culturally and sociologically (or in socio-psychological effect) something like what we call centuries. Whereas we would say the Spanish conquered Mexico five centuries ago, the Aztecs might say that world-shattering event happened ten bundles of years ago.
20 x 13 = 260. The 260 day sacred calendar is composed of intercalations of twenty named days and thirteen numbers. Its origin is lost in the mythical mists of time and is speculated to have existed as early as the Olmec period (the "mother" culture of Mesoamerica, circa 2000 bc - 100 bc). Since it is roughly the length of human pregnancy, some anthropologists speculate that this coincidence may have something to do with its origins, but, as with many hypotheses regarding ancient American civilization, the facts are unknown. What is known is that the 260 days are counted and named by a mixture of twenty names and thirteen numbers.
The names of the days in the Aztec/Toltec calendar are (in Nahuatl): Itzcoatl Ehecatl Calli Cuetzpallin Coatl Mictli Mazatl Tochtli Atl Ixcuintli Ozomitl Malinali Acatl Ocelatl Cuautli Cozcacuautli Ollin Tecpatl Huihuitl Xochitl, or, in English equivalents: Alligator Wind House Lizard Serpent Death Deer Rabbit Water Dog Monkey Grass Reed Jaguar Eagle Vulture Earthquake Flint Rain Flower.
written by Michael Arthur and Daniel Charles