Ancient Mesoamerica—the region stretching from central Mexico to El Salvador and northern Honduras, including Guatemala and Belize—had a turbulent history. One city-state after another rose to power and then collapsed, often relatively suddenly and for no obvious cause. From the Olmec, who inhabited the hot and humid lowlands of the Mexican Gulf Coast as early as 1200-400 b.c.e., to the Aztec, whose powerful and in many ways cruel empire centered on the Valley of Mexico in the central highlands was at its height at the time of Spanish contact, the archaeological record of the region bears witness to numerous and varied polities that rose and fell.
Despite this backdrop of social turmoil, common aspects of Mesoamer-ican ceremonial centers (such as ball courts, the setting for a ritualistic ball game) bear witness to common practices and beliefs—in other words, a common worldview. An essential and apparently unassailable aspect of this worldview was the calendar. Its basic structure was totally distinctive—it is unlike any other calendar system the world has seen—yet extraordinarily consistent, and persistent, through ancient Mesoamerica. It consisted of two interconnected cycles. The first, relatively unexceptional in itself, comprised an endlessly repeating cycle of 365 days divided into eighteen months of twenty days plus five additional days.
It is the other cycle that is extraordinary and gives the Mesoamerican calendar its idiosyncratic character. Also endlessly repeating, it contained 260 days, organized around thirteen numbers and twenty day names, but with each running continuously, like two interlocking cogwheels. Thus, for the Maya (for whom the twenty day names were Imix, Ik, Akbal, Kan, Chic-chan, Cimi, Manik, Lamat, Muluc, Oc, Chuen, Eb, Ben, Ix, Men, Cib, Ca-ban, Etznab, Cauac, and Ahau), the day 1 Imix was followed by 2 Ik, 3 Akbal, etc., round to 13 Ben, but then followed 1 Ix, 2 Men, etc., round to 7 Ahau, then 8 Imix, 9 Ik, etc. Every possible combination of number and day name would be covered, but in what seems to us a very improbable order, before the commencement of the next 260-day cycle. The names of the two cycles, as well as the month and day names within them, varied from one Mesoamerican culture to another, but the cycles themselves were quite invariable. And they were themselves intermeshed, resulting in a Calendar Round that only returned to its starting point after slightly less than fifty-two years, in other words, exactly fifty-two rounds of the longer (365-day) cycle and seventy-three rounds of the shorter (260-day) one.
In central Mexico the Calendar Round was known as the Xuihmolpilli, or “binding of the years.” The end of the cycle, when the years were bound, was a time of great fear. All fires were extinguished, houses were swept very clean and all rubbish removed. At an elaborate ceremony, commencing in the middle of the night (when the Pleiades crossed the meridian, according to one source), new fire was kindled in the heart of a sacrificed warrior, thus ensuring that the sun would reappear, at which point runners with torches would spread the new fire around the land. The great Templo Mayor in the center of the Aztec capital of Tenochtitlan was rebuilt six times, each rejuvenation involving the addition of an entirely new layer over the existing temple, thereby increasing its size substantially. It has been suggested that these episodes of rebuilding might well have been undertaken in preparation for the start of a new Calendar Round, although there is no direct evidence to support the idea. It is more generally accepted that they were ordered by successive new rulers.
The 260-day cycle was called the tzolkin in the Maya region and the tonalpohualli in central Mexico. Nobody knows its origins. While the 365-day cycle (haab for the Maya, xihuitl or xiuhpohualli for the Aztecs) was clearly related to the solar year, the tzolkin has no obvious astronomical derivation, although several different theories have been proposed. One suggestion is that it arose from observations of the zenith passage of the sun around the latitude of fifteen degrees (that is, at around the latitude of the Classic Maya site of Copan), where the interval between the two dates of zenith passage in a given year was, indeed, 260 days. However, the earliest inscriptions attesting to the 260-day calendar round, dating to the mid-first millennium b.c.e., come from much farther north, in the region of Oaxaca. We do know for certain that the 260-day cycle was of fundamental importance for div-inatory purposes. Each day had its omens, good or bad, and these were used to regulate a variety of sacred rituals as well as more general activities. The tzolkin is still used for prognostications among Quiche Maya peoples to this day.
Ancient Mesoamericans were tremendously concerned with fitting together cycles of nature—or to be more precise, cycles of the celestial bodies— into neatly repeating longer cycles. All the while, the 260-day cycle, itself apparently unrelated to any cycle directly visible in the skies, endured and formed part of this process. Some larger cycles fell out naturally, owing to (what we would see as) coincidences of nature. The most important of these is the fact that eight synodic cycles of Venus are very close to five solar years. The Mesoamericans knew the synodic period of Venus to be 584 days, and by this reckoning five Venus cycles are exactly equivalent to eight haab or xi-huitl years of 365 days. It follows that, since the number of 365-day years in two Calendar Rounds is divisible by eight, two Calendar Rounds must also be a whole number of Venus cycles: actually sixty-five of them. This coincidence of three cycles has been suggested as a reason that particular significance was attached to the end of every second Calendar Round.
Another astronomical coincidence is that three times the mean eclipse danger period, close to 173.3 days, which would be necessary knowledge for anyone hoping to predict eclipses, is equal to two 260-day cycles, so that the main danger of eclipses would recur around (every other occurrence of) the same three dates in the 260-day cycle. Yet another coincidence is the fact that the synodic period of the planet Mars is equal to exactly three rounds of 260 days. In the case of central Mexico, it is not always easy to pursue these ideas, since the threads of evidence are very indirect, but it is quite certain that the Maya took this process of cycle-matching to tremendous lengths: we know this from the Dresden Codex.
A number of religious texts both from before and from shortly after the conquest contain cosmograms—representations of the cosmos that can contain depictions of the gods, the four quarters of the world and their qualities, the path of the sun along the horizon, and the calendar, plus perceived interrelationships between them. A famous example in the Codex Fejervary-Mayer, a pre-conquest document from central Mexico, contains a pattern of dots in the shape of a Maltese cross which represents the entire 260-day sacred round arranged in twenty groups of thirteen. In form, this resembles many of the pecked cross-circle designs found in and around a number of central Mexican sites. It is not surprising, then, that the numbers of small holes forming the basic elements of such designs seem to include, much more frequently than would be expected by chance, calendrically significant numbers such as twenty, eighteen, thirteen, and five.
Another way in which concepts of number, calendar, space, and time may have been tied together in ancient Mesoamerica is manifested in what has become known as calendrical orientation. Systematic studies of the orientations of buildings and city plans, both in central Mexico and in the Maya world, have revealed clear but curious patterns of orientation preference. (Many Maya cities, for example, have their street grids oriented a few degrees clockwise of the cardinal directions.) These preferences included sunrise and sunset on dates whose significance would have followed, as for many peoples worldwide, from directly observable extremes in the motions of the sun—the solstices and the days of zenith (and perhaps also anti-zenith) passage. However, there are also notable regional preferences for other days in the year. Some of these seem to indicate the existence of horizon calendars in which key dates were those counted off from the solstices in intervals such as twenty, fifty-two, sixty-five, and seventy-three days, numbers that also arise in the context of the Calendar Round.
However, the apparent coexistence of the Calendar Round and horizon calendars raises an issue. Calendars based on the movement of the sun up and down the horizon are implicitly tied to the true solar year, whereas the 365-day cycle of the Calendar Round that became established all over Mesoamerica would have slipped against this by one day in every four years, and the discrepancy would have become evident over time. Since our knowledge of the Calendar Round comes from documentary and historical sources, while the evidence for horizon calendars relies more on the statistics of alignments, it is not easy to resolve this issue. One possibility that has been suggested is that the horizon calendars were older developments, precursors of the Calendar Round. Another is that the formal, ceremonial 365-day calendar and the pragmatic horizon-based one existed in parallel, rather like what is thought (by most scholars) to have occurred with the civil and lunar calendars in ancient Egypt.
In most respects, the Mesoamerican calendar reflected the cycles of na-ture—particularly observable astronomical cycles—directly. The only apparent exception to this was the 260-cycle tzolkin or tonalpohualli: if this ever did have such a basis, it became lost in the mists of time. Yet this sacred cycle, with its complex set of associated prognostications, lay at the very heart of Mesoamerican worldview and calendrics.
