Archaeology in PNAS

Area of the Puchituk Terminus at Caracol

I just found two Mesoamerican articles in the online-first section at the Proceedings of the National Academy of Sciences. It's great to see good archaeology receive high-profile coverage in places that are seen by a wide range of disciplines. These papers describe early steps toward larger research goals, although they tend to be phrased as if they were reaching those goals right now.

Chase, Arlen F., Diane Z. Chase, Christopher T. Fisher, Stephen J. Leisz, and John F. Weishampel
2012    Geospatial revolution and remote sensing LiDAR in Mesoamerican archaeology. Proceedings of the National Academy of Sciences (published online first).

Scarborough, Vernon L., Nicholas P. Dunning, Kenneth B. Tankersley, Christopher Carr, Eric Weaver, Liwy Grazioso, Brian Lane, John G. Jones, Palma Buttles, Fred Valdez, and David L. Lentz
2012    Water and sustainable land use at the ancient tropical city of Tikal, Guatemala. Proceedings of the National Academy of Sciences (published online first)

LIDAR!

The central portion of Angamuco

The first paper is a brief description of recent LIDAR mapping at the Maya city of Caracol and the western Mexican city of Angamuco. Most readers will probably already have seen some LIDAR maps; if not, check out this article and some of the other publications. These maps are absolutely incredible. Arlen and Diane Chase (and their crew) spent decades instrument mapping at Caracol, and they still had only covered a portion of the site. Now with one application, the LIDAR map covers the entire (huge) urban area, with high resolution and great accuracy. Arlen first showed me the maps two years ago and I was blown away. It is hard to express just how much of a leap forward this is for archaeological mapping, particularly in highly vegetated areas like the Maya lowlands. The PNAS paper only has a couple of images (see above); see some of the other publications, cited in that paper, for more images.

The Angamuco map, done for the project directed by Chris Fisher, is also pretty amazing (above). It is one of a series of west Mexican urban settlements built on lava flows. Some French teams have been working on other sites of this type, which have the potential to greatly illuminate our understanding of urban form (since many house foundations and other features can be mapped).

So what are the larger research goals that can be addressed with these and other LIDAR-mapped sites? Leaving aside the obvious goals of providing more details about individual archaeological sites, I am excited about this work because of the potential to advance our understanding of urban morphology in ancient cities. It is going to take some time to reach this goal, since we presently lack the methods to translate good maps (whether made with LIDAR or with old non-electronic instrument mapping, or with a compass and tape) into rigorous results about city layout and planning. It is striking to see high-tech spatial methods (LIDAR, various prospecting methods like ground-penetrating radar, NASA satellite imagery) used to make visually arresting maps, which are then interpreted in a subjective and impressionistic manner.

Perhaps the situation is analogous to provenience studies of artifacts. For many years, even decades, we have had good data on the places of origins of lots of artifacts, but few models or concepts on how to translate those data into reliable economic inferences. I have complained about this for many years, in various review articles and such. Methods and data often far out-run our interpretive approaches. Now, finally, archaeologists are working out methods for reconstructing things like market systems from artifact sourcing studies (see, for example, Garraty and Stark, eds, 2010, Archaeological Approaches to Market Exchange in Ancient Societies, Univ Press of Colorado). So, I hope that archaeologists and others will made the kinds of advances in studying urban form that are needed to really take advantage of the great maps produced by LIDAR (and other methods).

MAYA RESERVOIRS AND SUSTAINABILITY

Reservoirs in central Tikal

The second PNAS paper is a nice study of the construction and use of reservoirs at the Maya city of Tikal. Over many years, Vincent Scarborough has led an effort to show how the ancient Maya managed water resources, and the social context of water. His excellent study (The Flow of Power: Ancient Water Systems and Landscapes, 2003, SAR Press) helps put the Maya case into a broader comparative framework. The reservoirs at Tikal (see image above) have been known for a long time, but now Scarborough and his colleagues have learned how and when they were built and how they were used.

I am a bit skeptical about the sustainability argument of this paper. There isn't much of an explicit argument here. The implied argument seems to be that the schemes for water control and use identified by fieldwork were a form of sustainable land use, thereby permitting the city of Tikal to flourish for many centuries. Perhaps. That seems a reasonable notion, but how can it be confirmed or falsified? This is a causal argument (these practices caused -- or at least allowed and stimulated -- a long occupation). But to confirm this hypothesis, more cases and better interpretive models are needed. What would non-sustainable practices look like? Are there some cities that used major water control methods and lasted for many centuries, while other similar cities did not use the water technology and did not last as long?

It is difficult, perhaps impossible, to make a convincing causal argument from a single case. One minimally needs to consider the counterfactual case -- suppose that the rulers or builders of Tikal had NOT designed such clever water control features. What would have been the consequences? Perhaps an argument can be made that the city would not have lasted so long, or would not have grown so large, without these features. But even though this kind of explicit counterfactual argument can suggest a causal model, any real conclusions about ancient sustainable practices require a much larger sample of cases. I develop this argument in my 2010 paper in CAJ: my point is that archaeologists have data to address issues like urban sustainability, but we have yet to assemble rigorous samples and perform the necessary analyses to produce reliable results.

Research like that described in the paper by Scarborough et al in PNAS is important for understanding Tikal and for building knowledge about ancient systems of water control. It could also be important for generating findings about ancient sustainable practices, but to do this, it needs to be joined by many more studies to build a reliable base of information. This paper is an excellent step in that direction, but I think it is premature to make any claims about sustainability from single studies like this.