Aztec Tonalpohualli

The tonalpohualli pairs twenty named day signs, Crocodile, Wind, House, Lizard, Serpent, Death, Deer, Rabbit, Water, Dog, Monkey, Grass, Reed, Jaguar, Eagle, Vulture, Movement, Flint, Rain and Flower among them, with the numbers one through thirteen running independently alongside them, so a full combination of sign and number repeats only after two hundred sixty days, since twenty and thirteen share no common factor smaller than their own product. The cycle divides into twenty trecenas, thirteen day spans each opened by day one of a particular sign, and each trecena was held to fall under the patronage of a specific deity pair whose favor coloured the fortunes of everyone born within it.

The tonalamatl, literally "book of days," was the painted almanac priests called tonalpouhque consulted to read a child's day sign at birth and forecast the character and fate that sign carried, to choose auspicious dates for marriages, journeys and warfare, and to time the great state rituals against the day on which they fell. The two hundred sixty day count has no straightforward tie to any single astronomical period, and its true origin is uncertain. What is well attested is that the same cycle, under different sign names, structured the Maya tzolkin and calendars across Mesoamerica well before either the Aztec or the Maya state existed in the form the Spanish encountered.

Colonial Spanish sources, chiefly Bernardino de Sahagun's Florentine Codex, preserve the tonalpohualli in unusual detail precisely because Spanish missionaries considered it dangerous: the calendar was inseparable from the divinatory priesthood's authority, and understanding it was necessary to suppress it, so the very effort to eradicate the system is what left the fullest record of how it worked. The state sponsored priesthood that read the tonalamatl for the Aztec elite did not survive the conquest, and daily divinatory practice by trained tonalpouhque working from painted books ended with it.

The cycle's structure has not disappeared from Indigenous Mesoamerican life, though. Variants of the two hundred sixty day count are still kept by Maya daykeepers in Guatemala under the related name tzolkin, and among Nahua communities and Mexica revivalist movements the tonalpohualli itself has been reconstructed for personal and ceremonial use, most visibly as a source of individual day sign identity rather than as a state instrument of divination. The reconstructed modern practice is not a seamless continuation of the pre-conquest priesthood's calendar. It draws on the same colonial sources that preserved the system in order to recover a use for the calendar that Spanish suppression had broken.