Ancient Urban Sustainability

Why did some past cities flourish for many centuries, even millennia, while others grew and declined over a period of years or a decade?

Tiwanaku: sustainable city??

Archaeologists have an incredibly extensive set of data on ancient urban sustainability, but we have yet to pursue targeted analyses of those data. I think that someday we will be able to answer the question posed above, but we are not yet close to an answer. I am following a theme I first addressed in my 2010 paper, "Sprawl, Squatters, and Sustainable Cities: Can Archaeological Data Shed Light on Modern Urban Issues?" Cambridge Archaeological Journal 20:229-253. I make the same point for all three topics -- that archaeologists have relevant data, but have not analyzed it yet in ways that can contribute to contemporary debates on urban issues.

I assigned my 2010 article in my ancient urbanism class (advanced undergrad) a year ago. One perceptive student (Seven Tomek) asked why I wasted time describing what archaeologists had not done yet - why didn't I just go out and do the analyses? Well, if I didn't already have several other research projects that take up most of my research time, I would do that. But it will take considerable dedicated effort to turn existing archaeological data into systematic and useful findings that are relevant to contemporary urbanization.

The Yautepec Valley of Morelos

Here I will review one of the examples originally included in my 2010 paper: the longevity of settlements in the Yautepec Valley of central Mexico. This is based on a full-coverage regional survey that I carried out with two graduate students, Timothy Hare and Lisa Montiel (for details see our technical report or their dissertations). Actually, they did most of the work! For my 2010 paper I identified all "urban" sites located in the survey. This was a quick-and-easy definition: any site larger than the smallest Aztec city-state capital was counted as urban. The rationales is that we know the Aztec sites were functionally urban, so this was a convenient cut-off for earlier sites as well.

My measure for sustainability was longevity; that is, how long were cities occupied? This fits theoretical discussions in the sustainability literature that stress longevity as a marker of sustainability (e.g., Bernard C. Patten and Robert Costanza  (1997)  Logical Interrelations between Four Sustainability Parameters: Stability, Continuation, Longevity, and Health. Ecosystem Health 3(3):136-142). I arranged sites in chronological order, from the earliest urban sites (Late formative Period) up to the Aztec period. Here is the graph:

Longevity of urban sites in the Yautepec Valley. Each vertical bar is an urban site.

I should start out by saying that I have yet to carry out a systematic analysis of these data. My remarks here are impressionistic and suggestive, not definitive.There were several waves of urbanization. The first, in the Late Formative period (green bars), generated three cities that flourished for over a millennium. Their success is almost certainly due to their locations: adjacent to the the largest expanse of rich farmland in the entire Yautepec Valley. The biggest single wave of urbanization occurred in the Classic period (red bars), when the valley was conquered by an empire based at Teotihuacan. These towns probably organized the cultivation of cotton and its shipment to Teotihuacan. When Teotihuacan influence waned after a couple of centuries, these sites were abandoned (except for one).

Shortly thereafter, a period of lowered rainfall set in (yellow on the map), and few new cities were founded. The increased rainfall in the 12th century AD coincided with the arrival of the Aztec peoples in this area. A new wave of urbanization took place, first in the Early Aztec period, and then in the Late Aztec period. These new cities were small capitals of city-states. Most were then destroyed in the Spanish conquest of 1521.

While this description is too provisional and subjective to produce definitive results, a few implications can be drawn. First, a range of factors must be considered in explaining the longevity or success of ancient cities. These include soil quality, rainfall, imperial conquests, and local demographic processes. Second, different causal factors came into play at different periods. Classic period urbanization was part of imperialism, whereas earlier cities were formed and flourished for largely environmental reasons. Third, these results suggest that if archaeologists were to assemble parallel data form other survey projects, we would learn quite a bit about why some cities flourished for many centuries while others did not.

I deal with ancient urban sustainability in an earlier post:

Were ancient cities sustainable?

REFERENCES:

Hare, Timothy S.  (2001)  Political Economy, Spatial Analysis, and Postclassic States in the Yautepec Valley, Mexico. PhD dissertation Dissertation, Department of Anthropology, University at Albany, SUNY.

Montiel, Lisa  (2010)  Teotihuacan Imperialism in the Yautepec Valley, Morelos, Mexico. PhD dissertation Dissertation, Department of Anthropology, University at Albany, SUNY.

Smith, Michael E. (editor)  (2006)  Reconocimiento superficial del Valle de Yautepec, Morelos: informe final. Report submitted to the Instituto Nacional de Antropología e Historia.