How the Aztecs did math

See Science magazine for a fascinating paper on how Aztec surveyors measured agricultural fields:

Williams, Barbara J., and María del Carmen Jorge y Jorge
2008 Aztec Arithmetic Revisited: Land-Area Algorithms and Acolhua Congruence Arithmetic. Science 320:72-77.

For descriptions of the research by journalists, see:

http://sciencenow.sciencemag.org/cgi/content/full/2008/403/2

http://news.nationalgeographic.com/news/2008/04/080403-aztec-math.html

Aztec Royal Tomb

Last fall, archaeologists working near the Aztec Templo Mayor in Mexico City uncovered a huge carved stone monument with an image of Tlaltecuhtli, the earth god. Last week they scanned the area with ground-penetrating radar, which revealed several hollow chambers under the monolith. A date on the monument -- 10 rabbit -- corresponds to AD 1502, the date the emperor Ahuitzotl died. This could the tomb of Ahuitzotl, which would be a major find because no royal Aztec burials have been located previously.

You can listen to me talking about this on National Geographic News for August 10, 2007, on the NSG website (click on news for August 10; the interview starts about 7:30 into the show).

http://www.nationalgeographic.com/podcasts/ngnews.html

How is this relevant to Calixtlahuaca? Well, I was interviewed for an AP story about this by cell phone while supervising excavations high on the hill at Calixtlahuaca:

http://news.yahoo.com/s/ap/20070803/ap_on_re_la_am_ca/mexico_aztec_tomb

Also, it was Ahuitzotl's brother, the former emperor Axayacatl, who conquered Calixtlhahuaca for the Mexicca around 1475.

Now we have to wait for archaeologists to remove the huge (broken) monolith to see what is in the hollow chambers....

The 2007 Season is Done

I have been too busy to post to the blog for a while. We finished fieldwork in early July. As typically happens, we found all sorts of interesting (and time-consuming) things the final weeks of fieldwork. We excavated three burials the final couple of weeks, two with ceramic vessels as offerings, one without. We found a buried burned house with a collapsed burned daub wall covering 20 cm of charcoal—burned seeds, wood, and other plant material. In that excavation (unit 323), a trench just clipped the edge of the feature in the final days of fieldwork, so we were only able to excavate part of it. In a trench designed to document the stratigraphy of an agricultural terrace we found a nice stone pavement, with a dense midden deposit underneath.

All this activity, plus other issues of closing down fieldwork, have given me little time for the blog (but then how I find time to start a new blog for professionals and grad students called “Publishing Archaeology”? http://publishingarchaeology.blogspot.com/ I will quote Walt Whitman: “ Do I contradict myself? Very well, then I contradict myself. I am large, I contain multitudes.”).

We have moved our entire lab to the Colegio Mexiquense in nearby Zinacantepec, where we will be analyzing artifacts for the next few summers. Just a few closing facts, things that came up in the final weeks of the season. Our total of burned daub is over 500 kilograms (half a metric ton). What are we going to do with all this? Stay tuned. I will keep this blog open to report various project results as they become available and as I have time to report. Also on the daub, we have found that many of the wood house supports were made of maguey stalks (the impressions on freshly-cut maguey stalks match rather precisely the impressions on the burned daub).

The last task given to our excellent crew of local lab workers was to catalog the sherd disks. They spent over a day at it, and had to stop when we came to move the tables and chairs to the new lab. The catalog now includes over 1,600 sherd disks, and they still have about 25% of the collection to catalog.

I won’t be giving a paper on the excavations at the SAA meetings next year, because I was talked into giving a presentation on “Ancient cites: Do they hold lessons for the modern world.” It seems less important to report new fieldwork at the archaeology meetings now, since things can be posted so easily on the internet. Between this blog and more formal project reports and data on the project web site, interested people can keep up with the project.

This has been an experiment for me. If you particularly like this blog, let me know. If you think it is stupid and pointless, then please keep your opinions to yourself! (I once got an email from a high school student telling me that “my so-called web site is a piece of sh—“. I think she needed information quickly for a report due the next day and my site didn’t have what she needed.)

The haciendas of Calixtlahuaca

The ruins of several old haciendas can be found in and around the modern town of San Francisco Calixtlahuaca. Local lore tells of the burning of Hacienda Nova early in the twentieth century; today this one adobe wall segment from a storage building is the only standing wall. The traces of wall foundations are visible on the ground, and vitrified bricks (from high-temperature burning) litter the area. These ruins lie just outside our reconstructed urban boundary for the Postclassic city, on the west side. Most of the adobe walls of Hacienda Palmillas are still standing (see photo; with Cerro Tenismo—Calixtlahuaca—in the background). The open courtyards that were once hacienda work areas are now planted with maize. This hacienda is located north of the modern town, well outside of the archaeological site.

These haciendas are important to out research at Calixtlahuaca because they hold clues to the modern modification of the hillslopes and terraces of the site. After the Spanish conquest, the Postclassic city was abandoned and remaining inhabitants were moved forcibly into Toluca as part of the Spanish “congregación policy (moving or congregating natives into town centers). Spaniards moved into the area and set up haciendas, and by the late nineteenth century the haciendas owned most of the land around Calixtlahuaca (including all of the fertile valley floor). As Mexican haciendas go, these were quite modest in size, in architectural elaboration, and in their landholdings. In 1893 Hacienda Nova owned 6.02 sq. kilometers and Palmillas owned 6.88 sq. km. By contrast, the Hacienda La Gavia some 20 miles to the west owned some 640 sq. km. of land.

In the 1890s, peasant farmers started moving to the Calixtlahuaca area in large numbers (we are not yet sure why this happened; the data are from state and federal census documents). The only places left to farm were the slopes of Cerro Tenismo, covered with eroding remnant Postclassic terraces. The Postclassic terraces were too narrow to plow with teams of animals, so farmers removed one or more terrace walls to form larger fields to plow. Although this resulted in the destruction of much of the Postclassic terracing and houses, many ancient structures were in fact preserved for the future by the modern terracing. In order to level off their new larger fields, these modern farmers built up the lower sides of the fields with fill, burying and preserving the Postclassic deposits. We have managed to locate and excavate several structures and features buried this way.

I have been looking into historical data on local haciendas and demography in order to better understand the modern reworking of terraces and deposits at Calixtlahuaca. Unfortunately there seem to be few documents on these haciendas, and historians have done little research on the small agricultural haciendas in the Toluca area. We have made some progress, but many questions about the modern re-invasion of the archaeological site remain unanswered. But these are interesting ruins in their own right, and perhaps some historical archaeology is called for. I made the accompanying sketch of of Palmillas by filling in details not visible on our site orthophoto.

Help! We are inundated with burned daub!

Little did I know when I posted the May 14 entry on burned daub that we would soon be inundated with this stuff! We normally bring artifacts back to the lab in plastic bags, and when an archaeologist has a lot of bags, he or she uses a "costal" (a large flour sack) to carry them. In two of our excavations (units 315 and 317), the archaeologists (Angela Huster and Tim Brown) have had to use costales—sometimes more than one—just to bring back the burned daub from single excavated levels. We are running out of space in the lab to store this material, and it takes a long time to wash. It takes even longer to dry, and students have to step over piles of drying daub on the way to the bathroom and kitchen. We had better be able to make sense of this stuff to make up for all the logistical hassles in collecting, washing, storing, and studying it!

Salsa, Stone, and Pottery

The basic implement used in traditional Mesoamerican cuisine for making salsa is the molcajete. The word comes from the Nahuatl term molcaxitl, a combination of the words molli (sauce) and caxitl (bowl). Archaeologists are interested in these vessels from 2 perspectives—production and use. Evidence for the manufacture of molcajetes (in the form of basalt flakes or objects broken in the process of production) helps us understand craft production and its organization in ancient times. Evidence for the use of molcajetes (whole or broken examples in domestic deposits) is important for reconstruction of diet and household activity patterns.

The basic kind of molcajete used in Mesoamerica, from ancient times through the present, is the stone tripod bowl. This weekend the crew visited the village of San Andrés Cuexcontitlan (not far from Calixtlahuaca) to see contemporary molcajete producers at work. Many of the inhabitants of this village still speak Otomi, and linguists have done research here to improve their knowledge of this ancient language. The production of manos, metates, and molcajetes from basalt is a traditional craft that has been handed down from father to son for many generations. There are about 25 artisans in the village, and they work in small sheds set up next to a large basalt quarry (see photo).

One interesting result of our fieldwork is that we have found almost no stone molcajetes at all. This is a great contrast to Postclassic sites in Morelos and other parts of central Mexico, where stone molcajetes are a common domestic item. How did the inhabitants of Calixtlahuaca make their salsa (and guacamole, and other foods that require the grinding of chiles, tomatos, etc)? The answer is that they used ceramic tripod bowls with incised patterns on the base (see photo). This is a very common ceramic form at Postclassic sites in the Toluca area. The vessel in the photo was excavated at Calixtlahuaca by José García Payón in the 1930s. We have found few whole vessels, but we have many molcajete sherds (see photo), most of which are painted tripod vessels.

In spite of the lack of basalt molcajetes at Calixtlahuaca, the work of the artisans at San Andrés Cuexcontitlan is relevant and helpful to us in several ways. First, it is possible that some of our other basalt tools were produced in or near Cuexcontitlan. Basalt manos are fairly common, and we have a few fragments of metates. If we decide to pursue the question of basalt trade routes, we will want to return to these quarries and take samples (as well as look for possible evidence that the quarries were used in Prehispanic times). Second, information on the organization and technology of craft production at Cuexcontitlan can help us reconstruct ancient craft industries, because most archaeological interpretation is based on analogies with modern and historic cases. I don’t know of any modern studies of these artisans, and perhaps this would be a good topic for an ethnoarchaeologist. Third, it is very possible that some or all of the inhabitants of Calixtlahuaca spoke Otomi, and knowledge of modern Otomi peoples may help us understand the ancient city and its population.

I want to thank Sergio de Jesús and the other representatives of the Unión de Pueblos de Toluca for arranging out trip, and we owe a big thanks for Miguel Garduño Martínez and the other basalt workers of San Andrés Cuexcontitlan for sharing their information and their craft with us.

Wattle and Daub

We have been finding many chunks of burned clay in the three most recent house excavations (units 315, 316, and 317). These are burned daub, sometimes called “bajareque.” They are evidence of the use of wattle-and-daub construction in the houses at Calixtlahuaca. This is somewhat of a surprise, both in terms of the presence of this type of house in the Toluca Valley

and in the nature of the construction methods. Wattle and daub is a form of house construction that was used in virtually all parts of the world in ancient times, and in traditional ethnographic houses in tropical areas today. A frame is built of sticks or cane; this is the wattle. Then mud (daub) is applied over the frame. The mud dries and fills in the spaces between the wattle. When a wattle-and-daub house burns down, the daub (sun-dried clayey mud) is fired like any other ceramic material, and becomes hard and almost indestructible.

The photo shows some of the pieces of burned daub from unit 316. The first odd thing is that this kind of construction was used at all in the Toluca Valley. Most Aztec houses in central Mexico were built using methods and materials that are still found today in traditional peasant houses in the same region. The stone foundation walls and adobe brick construction of Aztec houses I’ve excavated in Morelos match precisely the foundations and walls of modern peasant housing in the area. We found small amounts of burned daub at these sites, and wattle-and-daub construction is still used today in Morelos for traditional kitchens and occasionally for houses. Aztec houses in the Valley of Mexico are also quite similar to modern peasant houses in the area.

Wattle-and-daub is rarely or never used in peasant houses today in the vicinity of Toluca and Calixtlahuaca; in fact I can not recall seeing this technique at all. Modern traditional houses are built of adobe bricks. I had figured that the climate was too cold and rainy around here. But the hundreds of pieces of burned daub shows that this conclusion was incorrect.

The second unusual thing about our burned daub is its form. The burned daub I have seen from Morelos and from other parts of highland Mexico (e.g., Oaxaca) shows the impressions of numerous closely-spaced thin sticks or canes. All pieces show one or more cane impressions. Although some of our daub looks like this, much of it is different. Some pieces show only a single stick impression (photo, upper right), and some show none at all. Many pieces have a very well-smoothed surface, and some pieces have several smoothed surfaces. At first we thought that the piece in the lower right of the photo was a fired brick (a technique not used prior to the Spanish conquest). But washing and close inspection showed that this is clearly burned daub, not brick. Overall, our daub more closely resembles construction methods in which the wattle provides a frame for the daub, but many pieces of daub were not in contact with the wood. The sketch shows a traditional wattle-and-daub house from Italy (modified after: Shaffer, Gary D., 1993, An Archaeomagnetic Study of a Wattle and Daub Building Collapse. Journal of Field Archaeology 20:59-75. This kind of construction was common in European Neolithic houses.

In reading about the archaeology and ethnoarchaeology of wattle-and-daub houses, I am struck by the fact that accidental fires are almost never sufficient to fully fire the daub. When archaeologists find extensive burned daub at a site, it is almost certain that the houses were deliberately burned down; additional fuel typically has to be added to the fire. Perhaps significantly, two or three of our excavations with abundant burned daub also have extensive areas of burned earth and charcoal. Who burned these houses and why? We are still looking for answers to these and other questions.