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The Aztec (Central Mexican) Calendar

6th Aug 2014

Mexicolore contributor Professor William L. Barnes

We’re sincerely grateful to Professor William L. Barnes, Assistant Professor of Art History, University of St. Thomas, Saint Paul, Minnesota (USA) for this detailed and hugely informative outline of the main workings of the calendar(s) of pre-Hispanic Central Mexico, and of their role in the daily lives of the Mexica (Aztecs).

What name would you give today? Is it a Monday, a Tuesday, a Sunday? If I were to tell you that we could meet for a cup of chocolate on a Sunday, how would you know which Sunday that might be? Is it the coming Sunday or the one after that? Context plays a role in this, to be sure, for if we were talking on Saturday, chances are our meeting would fall on the following day. But if we want to clarify which day, in particular, we are discussing we would then need to give that day additional names. We might give it a sequential name such as “next Sunday” or “the following Sunday” or we might place it within a bigger calendrical context by noting its position in the month: “the last Sunday of May.” Without really thinking about it, we regularly give our days many different names. More often than not, we select those names from different cycles that we use to mark time.
The most simple names that we give to days in what we might call the Western calendar, those mentioned above, come from a cycle of seven day-names that repeat endlessly: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday. In order to reference time more precisely we also select names and numbers from a much larger cycle, one made up of twelve month names and somewhere between 28 and 31 numbers. This cycle assigns a specific name and number to each day in any count of 365 (366 in leap years). So to be more precise about which day we will meet for chocolate I would specify the day using two different cycles, say, Sunday, 11 April. I could add more precision to this, if needed, by referencing larger cycles, clarifying that our meeting will take place on Sunday, 11 April, 2021 (or, perhaps, 2027).

In ancient Central Mexico, the Aztecs too had a system for marking time that was made of multiple cycles that include both day-names and day-numbers. The two most important of these cycles were the ritual calendar made up of 365 days, and the divinatory count that was comprised of 260 days. These two calendar counts operated simultaneously and served to uniquely identify each and every day in a 52-year period (18,980 days). While this would allow quite a bit of precision in identifying specific days within this long period of time (sometimes called The Calendar Round), Central Mexicans did not use a Long Count such as the Maya that allowed them to pinpoint days within a range of thousands of years. So while the Aztecs could use the interrelationship of these two calendars to identify any specific day in a 52-year period, one couldn’t say which 52-year period - The current one? The last one? The next one? - was being referenced.
This calendar system had its benefits and its drawbacks. Aside from the lack of a larger cycle of time to reference (larger than 52 years), one of the biggest drawbacks would be that you would have to wait 52 years for your precise birthday to reoccur! On the up-side, though, your name-day could sometimes fall twice in any one-year period. If you were lucky enough to live through an entire 52-year Calendar Round you could celebrate your name day seventy-three times.

The Xihuitl
The cycle most similar to our own 365/6-day calendar is what the Nahuatl speaking inhabitants of Central Mexico called the xihuitl. This is a Nahuatl term for year, but it also means turquoise or greenstone. This was convenient for Aztec artists, for they regularly used turquoise blue dots or small painted blue gems to represent years (see pic 3).
The count of this year, its cycle, was called the xiuhpohualli (turquoise count/reading or year count/reading). It was made up of eighteen twenty-day periods we now call veintena, based on the Spanish word for 20. However, if you do the math here, you will see that this only accounts for 360 days. What about the last five? For those, the Aztecs had a short little period they called the Nemontemi (see pic 4). This was a terribly unlucky period, and people were advised not to leave their houses or go wandering about during this time as they would surely trip and fall or have some other horrible thing happen to them. The Mexican scholar Alfonso Caso argued that this period came at the end of the year, but other scholars such as Rafael Tena have suggested that it fell elsewhere in the year. Indeed, some scholars have argued that the Nemontemi could have been used to stretch out the year in something similar to our leap days/ leap years that we use to keep our own calendar in sync with the solar year (that is roughly 365¼ days long).

The other eighteen veintena were called by specific names that, in some cases, referenced the great religious observances and festivals celebrated during their course or at their conclusion. Following Caso’s discussion of the year, and the lists compiled by Franciscan Friar Bernardino de Sahagún in the 16th century, these veintena were:
1) Izcalli (It is Revived)
2) Atlcahualo (Water is Abandoned)
3) Tlacaxipehualiztli (The Flaying of Men)
4) Tozoztontli (Small Vigil)
5) Hueytozoztli (Great Vigil)
6) Toxcatl (It is Dry)
7) Etzalcualiztli (The Eating of Maize and Beans)
8) Tecuihuitontli (Small Feast of the Lords)
9) Hueytecuilhuitl (Great Feast of the Lords)
10) Tlaxochimaco (Flowers are Given)
11) Xocotlhuetzi (The Fruit Falls0
12) Ochpaniztli (Sweeping of the Way)
13) Teotleco (Arrival of the God)
14) Tepeilhuitl (The Mountain Feast)
15) Quecholli (Flamingo/Spoonbill)
16) Panquetzaliztli (The Raising of Banners)
17) Atemoztli (The Water Falls)
18) Tititl (It is Wrinkled).

As scholars such as Paul Kirchhoff and Monroe Edmondson pointed out a number of years ago, it was quite common for different groups of people in Mesoamerica to start their annual count of the days at different times, and, it seems, some may have started their year count with different veintena. Some even started their 52-year calendar rounds in different years. As well, even in Central Mexico, various groups of people and political entities had different names for the veintena. This would be like the people living in the next city over from you using different names for the months. For example, as Alfonso Caso points out, in Tlaxcala the feast of Tlacaxipehualiztli was called Coaihlhuitl (Feast of the Serpent). Even, it seems, in Tenochtitlan some veintena had multiple names such as the tenth and eleventh veintenas of Tlaxochimaco and Xocotlhuetzi that were also celebrated as Miccailhuitontli and Hueymiccailhuitl (Small Feast of the Dead and Great Feast of the Dead).
While we might tend to think of these veintena as analogous to our months, they were, in fact, periods of time dedicated to specific religious ceremonies and the preparations for them. In general, the final day of each 20-day period served as the principal feast day for the entire period, but occasionally the festivities that closed the veintena had their start four, five, and even twenty or forty days earlier. The majority of what we know about these veintena and the religious rites celebrated during them comes from writings by Europeans in the sixteenth century such as the Dominican friar Diego Durán and the Franciscan friar Bernardino de Sahagún.

Another way in which these veintena might serve as false analogs to our current months is to think of them as merely a means of organizing time. They were, in reality, sacred periods of time dedicated to any number of supernaturals and while they did serve Central Mexicans as a means of organizing yearly activities (such as the collecting of tribute) their principal purpose was ritual in nature. Indeed, unlike our current months, these periods were not used to record dates or history of any sort and are generally absent from the Aztec visual record.
There were ways to reference specific veintena, particularly those that fell at very auspicious times, but this was done by referencing the days of the 260-day calendar that fell within them. This may seem odd to us today, as we are used to recalling past events that took place on specific days in various months such as the 4th of July, the 16th of September, or 5 November. Referencing these days by a smaller cycle of time would be unusual for us today. How often does one hear of the Mexican Día de la Independencia of 16 September referred to as “the third Sunday in September, 1810?”

Almost every Aztec veintena had as a central focus the celebration of a specific supernatural or groups of supernaturals. As laid-out by Caso, for the Aztecs of Tenochtitlan these included those related to the rain and water deities in some fashion (Atlcahualo [pic 6], Tozoztontli, Etzalcualiztli, Tecuihuitontli, Tepeilhuitl, Atemoztli), earth and agricultural deities (Hueytozoztli, Hueytecuilhuitl, Ochpaniztli, Tititl), the fire deities (Izcalli, Xocotlhuetzi, Teotleco), and supernaturals associated with hunting, warfare, and authority (Tlacaxipehualiztli, Toxcatl, Tlaxochimaco, Quecholli, Panquetzaliztli [pic 7]). In some cases more than one supernatural was celebrated in any veintena. For example, the fifth festival of Toxcatl celebrated both the omnipotent deity Tezcatlipoca and the tribal god of the Aztecs, Huitzilopochtli. Added to this complication is the fact that in any given year, there were a number of what the European friars referred to as “moveable feasts” related to the 260-day calendar that fell in each of the veintena and, at times, as claimed by Sahagún, superseded the ‘standard’ feast days of that particular period.

So where the Xihuitl may at first seem quite familiar to us with our year made out of months, it is quite different, both in its conception and use – not to mention its relative unimportance in recording history. When it was imperative that the particular date of an event be recorded, in Central Mexico, one would use the 260-day divinatory count, most commonly called the tonalpohualli.

The Tonalpohualli
The Nahuatl term for day is tonalli, and the verb pohua can mean either “to count” or “to read.” These two words, when combined, create tonalpohualli or “the day count”/”the reading of days.” This is the term usually used to reference the 260-day divinatory calendar. While this count did not correspond with the solar year (some believe it has lunar or Venus related base), it was the most important component of the Aztec calendrical system. When you encounter a date carved onto an Aztec monument (pic 8) or view a historical document with dates, those are days from the tonalpohualli.

As well, this calendar was quite important as a divinatory tool – that is, as a means of interpreting the future. It was also used to discover hidden meanings in current and past events. Last, and perhaps most importantly for the everyday folks of Central Mexico, it was used to name individuals and figure out what an individual’s future life might entail – for you were named after the day upon which you were born (more-or-less), your day-name being given to you when you were ritually bathed by a daykeeper (tonalpouhque) four days after your birth. As Sahagún tells us, it was believed that this day would then steer the course of your life.

Structure of the Tonalpohualli
The tonalpohualli was made up of the numbers 1-13 combined with 20 day-signs. The twenty day signs are generally depicted as pictograms – that is they are pictures of actual objects that we can recognize quite easily (i.e. dog, deer, serpent). Some are more ideographic, requiring some knowledge of Aztec culture in order to understand the various ideas and concepts they convey (i.e. the face mask of Tlaloc, the rain deity, being used to represent “rain”). The following are the 20 day signs with their rough English equivalent:-
1) Cipactli / Crocodilian
2) Ehecatl / Wind
3) Calli / House
4) Cuetzpallin / Lizard
5) Coatl / Serpent
6) Miquiztli / Death
7) Mazatl / Deer
8) Tochtli / Rabbit
9) Atl / Water
10) Itzcuintli / Dog
11) Ozomatli / Monkey
12) Malinalli / Grass
13) Acatl / Reed
14) Ocelotl / Jaguar
15) Cuauhtli / Eagle
16) Cozcacuauhtli / Buzzard
17) Ollin / Movement
18) Tecpatl / Flint
19) Quiahuitl / Rain
20) Xochitl / Flower

The way that one works through the count is to cycle through the numbers 1-13 while simultaneously moving through the 20 day-signs in order. Hence every count would start with 1 Cipactli and would continue on with 2 Ehecatl, 3 Calli, 4 Cuetzpallin, etc. until one reaches 13 Acatl. There the numbers would restart with 1 while the day signs continue on (1 Ocelotl, 2 Cuauhtli, 3 Cozcacuauhtli, 4 Ollin...). This creates a series of 13-day periods that are sometimes discussed as analogous to our weeks. We usually use the Spanish term trecena to reference them (as we did with 20-day veintena periods that make up the xihuitl), as we are not sure what they were called in Aztec times. There are twenty trecenas in all (each day-sign gets a turn as the first day in any 13-day period), with the first one being 1 Cipactli and the last one being 1 Tochtli. Do note that these dates are really numbered day-signs and they were not treated as objects in Pre-Hispanic times. Hence it is proper to say 5 Tecpatl (5 Flint) rather than 5 Tecpatls (5 Flints). This confused some writers back in the Sixteenth Century who discussed the days as plural entities.

Painting the Tonalpohualli
The easiest way to depict the tonalpohualli was to paint its 260-days in a tabular format, called an in extenso almanac by Elizabeth Boone. We have Pre-Hispanic examples of these in a couple of painted books, often called codices (plural of codex), that survived the conquest. These are the Codex Borgia and the Codex Cospi. The design of these almanacs should be quite familiar to modern folks who have worked with computer spreadsheets.
In the small Codex Cospi the in extenso 260-day count starts in the lower left hand corner of page one, one row up from the bottom (see pic 12) (the top and bottom rows of this ‘spreadsheet’ do not have day-signs, but, rather, include mantic and ritual information related to the five days listed between them). While this part of the document is damaged, we know that the first day-sign in this cell is Cipactli, as it is followed by Ehecatl, Calli, Cuetzpallin, and so-on (in the Cospi each day-sign is also accompanied in its cell by a little head that represents one of the nine so-called “lords of the night”). As this is a screen-fold document, that is, it is created as a long strip that is folded at intervals, the first 13-day period continues across pages 1-2 and then the second 13-day period continues across pages 3-4. This process continues until the end of page 8, and then we return to page 1, move up a row, and continue the count with the fifth trecena. In this way all 260 days (and all 20 trecenas) are shown in their totality over the first eight pages of the codex.

Trecena were quite important in the divinatory count, and most surviving tonalamoxtli (plural of tonalamatl “book of days” that recorded the tonalpohualli) include a section that reckons the 260-day count using these twenty 13-day periods. Again, these are usually presented in a cellular format that looks something like a Pre-Hispanic spreadsheet. A good example of one of these can be seen in the Codex Borbonicus, a large screenfold codex likely made shortly after the conquest.
On page 10 of the codex (pages 1-2 are, unfortunately, lost) we see the tenth trecena of the tonalpohualli, 1 Tecpatl (1 Flint). The day that starts this period can be found in the lower left corner of the page (pic 13 - click to enlarge). A single red dot for “1” sits just to the left of a red and white flint knife that represents the day-name “Tecpatl.” The list of days continues from left-to-right across the bottom of the page until we get to 7 Lizard in the last cell. The orientation of the page then shifts and the day-signs then continue vertically up the right side of the page with starting with 8 Serpent and concluding with the last day of this trecena, 13 Dog. To the right of each day-sign is one of the so-called nine lords of the night who shares the cell much as they did in the Cospi almanac discussed above. In the adjoining cells are figures considered to be the 13 lords of the day (or, lords of the numbers, since they stay in the same position throughout all 20 trecena) and their related birds and butterflies.
The largest single portion of these tonalamatl pages are dedicated to the patron deities of these particular 13-day periods. Here (pic 13, top left), the Borbonicus artist painted Tonatiuh, the solar deity, on the left, facing Mictlantecuhtli, lord of the land of the dead, on the right. The two are surrounded by paraphernalia and figures that relate to rituals celebrated at certain occurrences of these days.
In this one efficient page, then, one can see which deities presided over the trecena, aspects of rituals performed during this period, the deities who influenced the day and night portions of each day listed, as well as the birds by which one might take auguries.

The surviving Pre-Hispanic codices are full of almanacs like these, particularly those of the Borgia Group (Codices Borgia, Cospi, Vaticanus B, Laud, Féjérvary-Mayer, Tonalamatl Aubin, and the Aubin MS. 20 and Porfiro Díaz Reverse), and they would have been used to realize the various deities involved with different days related to religious and historical events as well as the happenings in one’s life.

The Calendar Round
As we do with our own calendars, the people of Central Mexico used their calendrical system to commemorate particularly important events and mark the extent of significant periods of time. As can be seen in the above discussions of the calendars there really was no such thing as a secular calendar for the Aztecs, all was religious, and as such, each important date usually has some significant religious meaning as well as potential historical importance. As well, since the two calendars, the xiuhpohualli and the tonalpohualli, did not share a common starting day or a common final day, the system was always in motion.
In Tenochtitlan, the Aztec capital, they recognized the year 1 Tochtli (1 Rabbit) as the year in which both calendars more-or-less started anew. However, they did not celebrate the completion of the 52-year cycle until the subsequent year, 2 Acatl (2 Reed) with the great Xiuhmolpilli (Binding of the Years) festival (pic 14). Some scholars have speculated that this change in the celebration date was linked to historically bad famines or droughts that occurred in the last few 1 Rabbit years before the conquest.

It may also be that the year 2 Acatl hosted the first unbroken 260-day tonalpohualli of the calendar round. You see, as the two calendars were not coterminal, often a tonalpohualli count that began in one year would continue on into the next. Some years actually hosted parts of three different tonalpohualli. The year 1 Tochtli, while it starts the new 52-year cycle, also begins with the tail-end of the last 260-day cycle of the previous year (see pic 15). It is not until the sixth veintena of Toxcatl that the first tonalpohualli of the new cycle begins, and it is not until the next year, 2 Acatl, that we encounter the first complete (that is, unbroken by any Nemontemi) tonalpohualli. From there, the xiuhpohualli continues on for fifty more years until the cycle comes to a conclusion in the year 13 Calli.

The years themselves, according to Alfonso Caso, were named for the day upon which they ended, their concluding day. In Caso’s calendrical reckoning, this annual ‘name-day’ is then followed by the five days of the Nemontemi. Mathematically, then, this limits the possible name-days of the years to four: Tochtli (Rabbit); Acatl (Reed); Tecpatl (Flint); and Calli (House) (see pic 16. Together these days are usually referred to as “year bearers.” Combining these four year-bearers with the numbers 1-13 (in the order presented above) then creates the 52-years of the Calendar round. This calendar round can then be broken into four quarters with each section led by either 1 Tochtli, 1 Acatl, 1 Tecpatl, or 1 Calli.

Uses of the Calendar
One of the principal uses of the calendar for everyday people was as a source of name-days for newborns, and in Book 4 of his monumental Florentine Codex, Bernardino de Sahagún provides us with an extensive account of what one could expect if named on certain days (usually grouped under the principal day of the trecena). For example, if you were named on the day 1 Ehecatl (pic 19), then your fate might be less than you might hope, for Sahagún tells us of “the eighteenth sign, named One Wind, and the evil, the bad, which was with it. It was said that those then born gained as reward an evil day sign.”
Much as we have astrologers today, the Aztecs had daykeepers (Sahagún calls them tonalpouhque, literally, “day readers/counters”), religious practitioners trained in interpreting the tonalpohualli almanacs contained in painted books. These daykeepers could ‘pull charts’ for individuals and organizations, interpreting the significance of one’s name-day (pic 17), specific historical events, or, even, helping plan future endeavors. Leaving on a long trading expedition? Consult a daykeeper to make sure that you leave on the most propitious day, and while there, ask to make sure that your arrival day will help you receive the best price for your goods. Planning a military expedition? Check to make sure that the regiment leaves on the best day so as to avoid trouble on the road and check to make sure that the day you storm the distant city is equally propitious. Thinking of getting married? Check with a daykeeper to make sure that you and your future spouse are compatible - you could avoid a lifetime of strife!

Of course, one of the other important uses of the calendar was to record dates, much as we use our own calendars. Yet the calendrical system employed by the Aztecs had an essential ambiguity. If I tell you that an event happened on 7 Ozomatli, you would then know what day it happened in the tonalpohualli count, but you would not know which day and in which year that it might have fallen (some days fell twice in any given year!).
This, then, likely contributed to what H.B. Nicholson referred to as “pattern history” where important events seem to fall on the same date, despite being separated by years and even centuries. An example of this would be the 1 Tecpatl departure of the Aztecs from their mythic homeland of Aztlan (supposedly in the 12th century) (pic 18) and a host of subsequent events that also fell in this year (or on this day), including the birth of the Aztec chief deity Huitzilopochtli, the seating of their first tlatoani Acamapichtli (in the 14th century), and the victory in their ‘war of independence’ against Azcapozalco (in the 15th century) among other important events. Since most folks would know of at least one or more of these historical events in the past, it was a quite efficient way to mark a contemporary event as highly important if you could manage to have it fall on (or, perhaps, near) that important day (or in a year with that date as a year-bearer).

Living in Harmony with the Calendar
So can you think of a date that is important to you such as your birthday, a religious holiday, or an important political date. Do you think that you could plan to have future events fall on that day if possible? Could you schedule it so that every important date in your life fell on your birthday? If you were wealthy and powerful enough you just might be able to do so. What if you believed that a specific date in the year was particularly lucky, say 7 September. Would you expect your favorite football team to always win on that day? What about your favorite racehorse?Would you always buy your lottery ticket on that day?
This is, at least in part, the role that the calendar played in the life of the Aztecs. As the calendar was, in essence, well over 18,000 days long, you would need the help of a specialist to help tease out its nuances, but certain days, to be sure, were probably well known as being more dangerous (like the 1 Ehecatl day mentioned above - see pic 19) or being rather lucky (like 1 Cipactli that starts the tonalpohualli). Since, as Mary Miller has pointed out, the 260-day calendar roughly echoes the human gestational cycle, you could even, as a parent, try to plan-out when your child might be born! As things were believed to usually regress to some type of pattern, you could hopefully use the skills of a tonalpouhqui to discern what dangers might lie in wait for your so that you could schedule your life in order to avoid risk wherever possible.

Q. What do you call someone who’s obsessed with reading Aztec codices?
A. An almaniac...

Learn more about the veintenas...

Comments (4)

Todd H. Holmes

31st Jul 2019

Comparing the trecenas between The Codex Borgia (Aztec) with The Codex Nuttall (Mixtec) I noticed a similarity in the design of the Trecenas. Are the pictograms the same? Or do they have a different meaning?

Mexicolore

It’s generally accepted that the Codex Borgia is Mixtec, NOT Aztec, so it’s to be expected that the writing style will be similar to that of the Zouche-Nuttall.

felipe garcia

10th Jan 2019

i am thankful for all your presentations on the Aztec and Mayan calendar, they have been very informative. i am writing not only to thank you for your work but also to ask for assistant in delivering to the world more information regarding their sciences, math and arts of the Mesoamerican Calendars. I have been choosen to perserve this forbidden knowledge and the only way i know how to perserve it. Is to teach as many as i can so history can know my people real achievements. So if you can help me do this, please contact me and we go from there. Neh Ehua

Kolt

3rd Oct 2016

Thanks so much for the follow-up, Ian! I’m looking forward to reading Brotherston’s work on the subject.

Kolt

28th Sep 2016

Wonderful article! Professor Barnes does mention ‘moveable’ feasts and observences, and I wondered if these other festivals were documented with any details such as names, frequency, and practices?

Mexicolore

We strongly recommend you consult a superb in-depth study of the feasts cycle, namely Gordon Brotherston’s ‘Feather Crown: the Eighteen Feasts of the Mexica Year’ (British Museum Press, 2005).

Mexicolore contributor Professor William L. Barnes