Oaxaca News//Viva Oaxaca order form//Home page//Viva Oaxaca contents

ARCHAEOASTRONOMY at MONTE ALBAN

Mysterious Monte Alban

Monte Alban lies just six miles from Oaxaca. It occupies the crest of a mountain that the Zapotecs leveled to create a vast plaza on which they built pyramids, temples, ball courts and tombs. Archaeologists tell us that it was founded around 500 BC and occupied for some fourteen centuries. At its zenith during the first centuries A.D., the ceremonial center and its immediate surroundings may have been home to up to 25,000 people; at that time, it was larger than any European city. Monte Alban was abandoned around 850 AD. Nobody really knows why. It's a beautiful and fascinating place that richly deserves its designation as a UNESCO World Heritage Site.

While most of the structures are rectangular and are aligned within a few degrees of north, one oddly shaped edifice stands out--Building J. It occupies the south end of the great plaza. The building is shaped like the prow of a ship (or, if you will, an arrowhead, or home plate in baseball), and is tilted by just about 45 degrees from all the other buildings. The triangular end points southwest. Like most large Mesoamerican structures, Building J is like an onion, with more recent layers covering older ones. It seems to have been started sometime before 250 BC.

From the time of its discovery, archaeologists have speculated that building J served as an astronomical observatory. This seems reasonable, given its unique shape and orientation, and the fact that all the great Mesoamerican cultures maintained extremely intricate and accurate calendars, structured their agricultural and religious practices, plus political decisions, around key dates, and attached great significance to certain astronomical phenomena, such as the first appearance of selected stars or star clusters, for example the Pleiades, or the complicated motions of the planet Venus.

An astronomer eyes the stars--from the Madrid Codex

The question is, what kind of observations might the ancient Zapotec astronomer-priests have made from Building J?

In his book, Skywatchers of Ancient Mexico, astronomer Anthony Aveni presents a fascinating theory that offers at least a partial answer to this question. His theory is based both on the astronomical alignments of Building J (and Building P across the plaza), and on his knowledge of what kind of celestial events skywatchers at other ancient American sites were interested in.

A view of Building J. The arrowhead points to the southwest.

Aveni's calculations show that in 250 BC, observers sighting along Building J's arrowhead during part of the year would have watched the bright Southern Cross drop below the horizon. He notes that this constellation, which was seen as a great bird, was important throughout Mesoamerica. Feasts were timed to its appearances and disappearances, and it's reappearance was thought to auger good crops and healthy children.

The back of the building may have been even more important. A sightline through a prominent doorway at the top of the structure points directly to an opening near the top of the grand staircase of a structure along the east side of the plaza, Building P. That opening leads into a small, dark chamber. The ceiling of that chamber is pierced by a vertical shaft. Twice a year, on May 2 and August 10, the sun passes directly overhead at high noon, and for a few moments projects a blindingly bright beam into the chamber. This phenomenon is called the zenith passage, and marked key moments in the year.

Building J with Building P in the background, to the right of the dark square

According to Aveni, there's at least one more key alignment. A priest standing in the doorway of building J before dawn on May 2, 275 BC and looking towards the horizon through the doorway atop Building P would have seen the first yearly appearance of Capella, the sixth brightest star in the sky.

Here's the scenario that Aveni envisions: After nights of patient observation, the astronomer-priest on Building J sees Capella rising over Building P just before dawn. He can then be sure that at noon that day the sun will pass directly overhead, pouring light into the sacred chamber inside Building P. He can ordain the proper ceremony for that key moment of the year. We have no way of knowing just what that ceremony was (although Aveni quotes a beautiful description of a Zuni ceremony for "pulling down the sun" on the day of the zenith passage at Zuni Pueblo, in New Mexico), but we can be reasonably sure that in one way or another it maintained the sacred, ordered relationship between the cosmos and the culture.

Most guides and guidebooks say that Building J is unique in all of Mesoamerica. That's not strictly true. Aveni points out that there's a smaller version of Building J at Caballito Blanco, an archaeological site about 30 miles east of Monte Alban. That arrow-shaped building shows similar kinds of astronomical alignments, although it points to a different bright star--Sirius--and could have been used to mark different moments in the year, for example the first days of summer and winter.

"Aside from these two buildings," writes Aveni, "no other example of such a shape is found in all of Mesoamerican architecture."

Oaxaca News//Viva Oaxaca order form//Home page//Viva Oaxaca contents