Dr. Stephen Kowalewski will conduct archaeological fieldwork in Mexico to study ancient population growth, collapse, and environmental degradation. The work will address the following question: did high population density lead to the destruction of the environment (chiefly though soil erosion), or was it the opposite, that high populations actually maintained a stable landscape and that it was abandonment and the consequent lack of maintenance that led to environmental degradation? The study area of Coixtlahuaca is crucial because it was a major prehispanic kingdom, an agricultural breadbasket, a trading center of Mesoamerica-wide renown, and a province conquered by the Aztecs. It is little-known archaeologically. Previous archaeological studies of nearby regions show a slow-down and some local abandonments about 1 AD, a major abandonment in several areas about AD 600, and very high population levels just before the Spanish conquest (AD 1521). Based on the pilot studies by the research team in 2008 and 2009, Coixtlahuaca may have gone through similar cycles of growth and collapse. The project will study growth and abandonment, not just at the last population peak and the Colonial-period collapse, but for the two earlier contractions: Did population growth in those earlier times lead to degradation of the environment or was the landscape relatively stable until abandonment? The project will use methods from multiple disciplines to measure population, land use, and environmental change. Geomorphology will describe cycles of hillside erosion and valley-floor deposition. Non-destructive geophyscial and geochemical techniques will aid in tracing buried sites and in estimating population density. The project will carry out a systematic archaeological survey of the whole Coixtlahuaca basin (about 400 sq. miles) to find all visible habitation and other sites. The project will use radiocarbon, optically stimulated luminescence, and ceramic style dating.
This project will result in systematically collected data on hundreds of previously unknown archaeological sites, many of them large and well preserved. This information will be useful for a long for cultural heritage management as well as for evaluating new scientific hypotheses. The project will also train young archaeologists in current standards for regional survey, geophysical applications, and local community relations. The study will respond to the considerable interest among local citizens in the history of the people and the environment in Coixtlahuaca and the Mixteca Alta.
The project investigated environment and human population change over the last 12,000 years in the Coixtlahuaca valley, Oaxaca, Mexico. This region is significant because it was home to a major kingdom and international market at the time of the Aztecs, 500 years ago. But now the land is extremely eroded, unproductive, and deserted. How could more than a hundred thousand people have sustained themselves on land that today seems incapable of supporting 10,000 inhabitants, and how did they do it? Local citizens asked us this five years ago. We set out to provide answers because this problem seems to lie at the root of the rise and fall of urban civilizations, not just here but generally. We proposed to relate human population to cycles of stability, erosion, deposition, and stream downcutting, extending back 10,000 years ago, before people were farming. The project brought together archaeologists, geomorphologists, and experts in non-destructive remote sensing. We spent six months doing field and lab work in Coixtlahuaca, and many more months analyzing the data. We found 391 archaeological sites, most never described before, and dated their occupations using the styles of the abundant potsherds on the surface of the ground. Outstanding among these are rock art sites, one of the longest continuously occupied large towns (700 BC-AD 500), a spectacular city perched high on the peaks of a mountain where we mapped over 700 residential terraces, fortified places, and the ancient capital of Coixtlahuaca which was one of the largest cities in Mesoamerica, covering 12 square miles. The project produced a GIS database, a relational database, forms for all archaeological sites, artifact collections, radiocarbon dates, an extensive photographic record, soil samples, prospection records, maps and drawings, reports, presentations, and publications. We made three major discoveries about the history of human settlement: 1) The control of water and soil by terracing did not develop gradually or with the pressure of population, but suddenly with the first farming and sedentary life, at about 1500 BC. This result comes from studying profiles of stream banks where we found and radiocarbon dated ancient check-dams. 2) Between 700 and 300 BC Coixtlahuaca had some of the biggest towns in Mesoamerica. The population was sustained by an already-sophisticated agricultural system. This finding was not anticipated. As part of this project, colleagues from the Universidad Nacional Autónoma de México (UNAM) used ground penetrating radar, magnetometry, and electrical resistivity to find the buried remains of houses. We recommend one of these places for thorough excavation because recovery of a whole settlement from this early time is rarely possible. 3) Population reached another peak beginning about AD 1300. Perhaps 200,000 people lived here at that time—20 times today’s population. The UNAM team found many buried house remains, supporting these ballpark estimates of high population densities. Check-dams and terraces were ubiquitous. This was a landscape shaped by people. Images of intensively terraced places such as in Bali or Ifugao approximate how the Coixtlahuaca valley looked 500 years ago. We have gone a long way toward answering the original question. A place now barren was in the past populous and rich because people had terraced the land to retain water and soil. This was an urbanized society supported by a commercial economy. The form of government was the city-state. Households maintained the agricultural system and were tied to each other and to the land through community-level institutions. What happened? In essence, the thousands of terraces that had retained rainfall, streamflow, and soil were abandoned in the unforeseen and catastrophic events of the 1500s-1700s: the 90% population loss due to disease, the congregation of remaining people into compact villages, over-grazing by sheep, goats, and cattle brought from Europe, the collapse of the commercial economy, and the blows to the social institutions that bound people together and to their fields and their water. Abandoned hillside terraces and check-dams broke through. The upper layer of carbonate-rich sediments was exposed, and left unmanaged, has turned to white stone. Sediments accumulated on the valley floor or were flushed out of the basin. Streams cut down as much as 16 meters. The scientific conclusion is widely applicable: In human-environmental history, natural processes are ever-present but people are the prime movers. We have more to say about this in publications now in preparation. Apart from the more theoretical results, our project has provided public lectures, factual reports, and recommendations to people and institutions involved with administration, education, cultural heritage, and land/water management in eleven municipalities. The project provided mutually beneficial training for eleven young professionals from the United States, Mexico, and Russia. This project shows how archaeology, working with other disciplines, can improve the understanding of how people maintain viable agricultural systems even with large and dense populations.
