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Liber VII · Divination

Liber VII · Divination · Chapter VII: Mayan & Aztec Astrology

The Aztec Tonalpohualli: Day Signs and the Book of Days

The Aztec tonalpohualli explained: the 260-day count of 20 day signs and 13 numbers, the tonalamatl books of fate, the day-counters and birth divination.

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The tonalpohualli ("count of days") was the 260-day sacred calendar of the Aztecs and other Nahuatl-speaking peoples of central Mexico, formed by combining twenty named day signs with the numbers one to thirteen. Professional day-counters read it in painted screenfold books called tonalamatl ("books of days") to determine the fate of newborn children, to choose times for marriages, journeys and rites, and to interpret omens. It was the central instrument of divination in Aztec society at the time of the Spanish conquest.

The 260-Day Count§

The 260-day count was not an Aztec invention. It appears in Zapotec inscriptions of the first millennium BCE and was used throughout Mesoamerica, by the Maya (who called it, in modern scholarly usage, the tzolk'in), the Mixtecs, the Zapotecs and the peoples of the Valley of Mexico; our article on Mayan astrology discusses its origins and the possible reasons for its length. The Aztecs, who dominated central Mexico from the fifteenth century until 1521, inherited it from earlier Nahua and other peoples.

The twenty day signs, in their usual order, were Cipactli (Crocodile), Ehecatl (Wind), Calli (House), Cuetzpalin (Lizard), Coatl (Serpent), Miquiztli (Death), Mazatl (Deer), Tochtli (Rabbit), Atl (Water), Itzcuintli (Dog), Ozomatli (Monkey), Malinalli (Grass), Acatl (Reed), Ocelotl (Jaguar), Cuauhtli (Eagle), Cozcacuauhtli (Vulture), Ollin (Movement), Tecpatl (Flint), Quiahuitl (Rain) and Xochitl (Flower). The numbers ran from one to thirteen alongside them, so that the count began with 1 Crocodile, 2 Wind, 3 House, and so on to 13 Reed, after which came 1 Jaguar. Only after 260 days did 1 Crocodile return.

The day signs are ringed around the centre of the famous Sun Stone found in Mexico City in 1790, which is often called the "Aztec calendar," though it was a monumental image of cosmic time rather than a working calendar. The site's Aztec horoscope pages describe each sign, from Cipactli to Xochitl.

Trecenas, Patrons and the Lords of Time§

The 260 days were divided into twenty periods of thirteen days, known to scholars by the Spanish word trecena. Each began with the number one and took its name from its first day, such as 1 Crocodile or 1 Jaguar, and each was placed under one or two patron deities. The patrons of the trecenas were major gods of the Aztec pantheon, including Quetzalcoatl, Tezcatlipoca, Tlaloc and Xipe Totec, and their character coloured the whole period.

Each day also had its own patron, and was accompanied by one of thirteen Lords of the Day and one of nine Lords of the Night, the latter beginning with the fire god Xiuhtecuhtli. Many days were associated with birds or flying creatures as well. A diviner reading a day therefore weighed several overlapping influences: the sign, its number, the trecena and its patron, and the lords of the day and night. Numbers mattered: in general middle and higher numbers were considered more favourable than low ones, though there were many exceptions.

Besides the 260-day count, the Aztecs kept a 365-day solar year, the xiuhpohualli, of eighteen twenty-day months followed by five nemontemi days regarded as empty and dangerous. The two counts meshed every fifty-two years, a period marked by the New Fire ceremony, last celebrated before the conquest in 1507. The wider religious setting is described in our article on Mesoamerican religion.

The Tonalamatl: Books of Fate§

Aztec diviners worked from painted books, made of deerskin or of bark paper folded like a screen and read section by section. The books recorded the days of the count with the images of their gods and symbols, laid out so that a trained reader could locate any day and see the forces governing it. The Spanish called such books libros de las suertes, "books of fates."

Only a handful of pre-Hispanic and early colonial divinatory books survive. The Codex Borbonicus, now in Paris, begins with a tonalamatl in which each trecena occupies a page, showing its patron deities in a large panel beside its thirteen days and their lords; whether it was painted just before or just after the conquest is debated. The Codex Borgia, in the Vatican Library, is the most elaborate of a group of pre-Hispanic manuscripts, probably from the Puebla-Tlaxcala region, that set out the 260 days in many different arrangements for different kinds of prognostication. The Codex Fejérváry-Mayer, in Liverpool, opens with a celebrated diagram distributing the days among the four directions and the centre. Elizabeth Hill Boone's Cycles of Time and Meaning in the Mexican Books of Fate is the standard modern guide to how these books were organised and read.

The Day-Counters and Birth Divination§

The specialist reader of the books was the tonalpouhqui (plural tonalpouhque), "one who counts the days." Our fullest description of their work comes from the Franciscan friar Bernardino de Sahagún, who in the mid-sixteenth century worked with Nahua elders and students to compile the encyclopaedic General History of the Things of New Spain, preserved in the Florentine Codex. Its fourth book, devoted to the "soothsayers," goes through the trecenas and says what fortune each day brought to those born on it.

When a child was born, the family summoned a day-counter, who examined the day sign and its associations and pronounced on the child's character and prospects. Some fates were favourable, such as becoming a skilled ruler, warrior or craftsperson; others threatened poverty, illness or misfortune. Those born on 2 Rabbit, for example, the day of the pulque gods, were said to be inclined to drunkenness. The bathing and naming ceremony that followed could be moved to a more favourable day within the same trecena if the birth day was unlucky, so a bad fate was not entirely fixed. The Nahua concept of tonalli, a vital force associated with heat and the sun and received at birth, linked the day to the person's very being.

Day names often became personal names. The Toltec culture hero Topiltzin Quetzalcoatl was known as Ce Acatl, "1 Reed," and in the neighbouring Mixtec region rulers were commonly identified by their birth days, as in the case of the eleventh-century lord known as 8 Deer Jaguar Claw. The same logic of naming by birth date is found in the Chinese zodiac and in Indian birth-star names.

Election, Omens and the Fate of Empires§

The count was also used to choose times. Merchants waited for favourable days to set out on expeditions, warriors and rulers timed campaigns and ceremonies, and marriages required the agreement of day-counters for both families. Sahagún's informants also described a large body of omens, from the cries of certain birds to the appearance of wild animals in the city, whose meanings were interpreted alongside the calendar. Aztec cosmology placed the present world in the era of the Fifth Sun, named 4 Movement (Nahui Ollin), which was expected to end in earthquakes.

The calendar has also become part of the story of the conquest. Hernán Cortés arrived in 1519, a year named 1 Reed, which was also Quetzalcoatl's calendrical name, and later sources claim that Moctezuma took him for the returning god. Many modern historians, including Camilla Townsend and Matthew Restall, regard this story as a post-conquest construction rather than a belief documented at the time, though the coincidence of the date is real. Like the prophecy stories of other conquests, it shows how calendrical divination was reinterpreted after the event, a theme discussed in our article on divination.

Suppression and Survival§

Spanish missionaries regarded the books of fate as idolatrous and destroyed many of them, and the public practice of the day-counters was suppressed. Yet friars such as Sahagún and Diego Durán recorded the system in detail, partly so that confessors could recognise it, and the 260-day count continued in secret in some places. It survives today among several indigenous communities, especially among the K'iche' and other Maya of highland Guatemala and among some Mixe, Zapotec and Chatino communities in Oaxaca, where daykeepers still use it for prayer, healing and divination.

Since the late twentieth century the Aztec day signs have also been used in popular "Aztec astrology," which assigns each person a day sign from the date of birth on the model of Western horoscopes. These modern readings draw on the colonial sources but simplify them considerably, since the original practice weighed the number, the trecena and its patrons, the lords of the day and night and the judgement of the day-counter.

Frequently asked questions§

What is the tonalpohualli?§

It is the Aztec 260-day ritual calendar, formed by combining twenty day signs with the numbers one to thirteen. Each day had its own character and patron deities, and the count was used for divination, naming and choosing auspicious times.

What is a tonalamatl?§

A tonalamatl, "book of days," is a painted screenfold manuscript that laid out the 260-day count with its deities and symbols. Diviners consulted it to interpret birth days and choose times; the Codex Borbonicus and the Codex Borgia are the best-known surviving examples.

Is the Aztec Sun Stone a calendar?§

Not in the working sense. The Sun Stone shows the twenty day signs around a central face and the symbols of the cosmic eras, but it was a monumental sculpture expressing Aztec ideas of time and the sun, not a device for counting days.

How is my Aztec day sign determined?§

Modern correlations convert a birth date to its place in the 260-day count, giving a number and one of the twenty day signs. Scholars use a standard correlation between the Aztec and European calendars, though some details of the correlation remain debated.

Sources and further reading§