PROVIDENCE, R.I. [Brown University] —Stephen Houston, a professor of social sciences at Brown University, helped lead a groundbreaking project that used cutting-edge laser technology to survey 2,100 square kilometers of Guatemalan forest by airplane, rewriting the understanding of Maya civilization in the process.
The ambitious project, undertaken in 2016, was funded by Guatemala’s Fundación PACUNAM (a Guatemalan nonprofit focused on promoting scientific research, conservation and sustainable development in the Maya Biosphere Reserve) and included more than 30 scientists and archaeologists from leading academic institutions worldwide. The work was authorized by Guatemala’s Ministry of Sports and Culture.
Using LiDAR (Light Detection and Ranging) technology, researchers were able to penetrate thick foliage to see what lay under the surface of the rainforest. An active remote-sensing technology, LiDAR uses laser pulses to map land cover and ground surface in 3D space. Houston said the technology emits beams of light, some of which reach the surface, and the sensor captures a “cloud” of spatial information. Some 5.2 billion beams hit the surface, scanning the terrain from six angles and revealing otherwise invisible details of ancient landscapes.
In essence, cities were “stripped” of concealing vegetation, Houston said. What the LiDAR team saw suggests that the Maya civilization was far more populous and complex than previous research indicated, and that it was, in its infrastructure, among the most sophisticated civilizations in world history.
Houston has spent decades researching the Classic Maya civilization, including excavations at the city of El Zotz and the ruins of Piedras Negras, Guatemala. Houston said the LiDAR initiative differed sharply from traditional fieldwork, which has involved cutting through the jungle to allow access for cumbersome survey equipment.
The findings from the LiDAR survey, Houston said, were breathtaking. They revealed more than 64,000 dwellings and structures that increase the estimated population of the area to about 7 to 11 million. They also showed human-made features related to intensive agricultural production, extensive road construction, fortifications and other features.
The project was the subject of a National Geographic article and documentary, and Houston and his colleagues, including anthropologists Tom Garrison of Ithaca College and Marcello Canuto and Francisco Estrada-Belli of Tulane University’s Middle American Research Institute, published their research in Science on Sept. 27.
The study, “Ancient lowland Maya complexity as revealed by airborne laser scanning of northern Guatemala," describes how the team’s work has spurred a comprehensive revaluation of the demography, agriculture and political economy of ancient lowland Maya civilization.
Here, Houston talks about the findings and their implications.
Q: As someone who has completed many excavations at Maya sites in Guatemala, can you describe what it was like to first see the maps created by the LiDAR survey?
Quite literally, it took my breath away. I’ve been mapping in arduous conditions since the early 1980s. This is often sweaty, dangerous work — using machetes to cut sight-lines in the jungle, balancing measuring devices in mud and heavy rain, stretching tapes along ragged edges of mounds. At times, to my embarrassment, I have walked right by, or over, fairly substantial buildings. Vegetation and ground cover make them easy to miss.
Of course, there’s no substitute for fine-grained appreciation of ancient sites — at some point, archaeologists have to see them on the ground. But the LiDAR offered an unprecedented view, as though a “magic lens” had filtered through all that obscuring forest, or, as another analogy, a fogged window had been wiped clean. We could see continuous landscapes, along with wholly unexpected features in swamps, hilltops or broken terrain that no specialist had ever visited before.
Entire cities, including the great metropolis of Tikal, were suddenly laid bare, down to their smallest buildings and most distant hamlet. I won’t have this experience again... at least not until the next flights are flown!
Q: What was most surprising to you?
In “our” zone, where I’ve been collaborating with Tom Garrison of Ithaca College, we saw several things that took us aback. One was a set of sprawling fortifications with concentric embankments, moated areas, ridge-top cisterns, perhaps to withstand sieges, and palaces protected by walls and what must have been gates. Before LiDAR, we didn’t have a clue that these existed, despite walking over parts of them during preliminary exploration. They extended over at least six kilometers. An early city called El Palmar seemed now to be 70 times larger than we had suspected, with raised fields for agriculture. An “isolated” royal palace had an extensive swath of settlement extending a kilometer or more.
What intrigued us too was the discovery of what we called “cave communities.” These were sinkholes with clear caves in them and with buildings nearby as though to serve or monitor these depressions and breaks in the surface. Tom and I suspect we’re looking at cacao or chocolate plantations for a kind of “money that grows on trees,” a food of immense value to the ancient Maya. The sinkholes provided conditions of concentrated humidity and the shade that cacao plants crave.
And then the looting. It’s no surprise that most Maya cities are Swiss-cheesed with trenches by tomb robbers. But the LiDAR showed the precise location of each and every one of these pits, giving us a powerful tool for evaluating such damage. In cleaning them out, we will also have a way to date buildings and to determine their ancient use and history.
Finally, Tom and I were fascinated by what may be a distinct “signature” to different periods of time. Earlier constructions from the beginnings of Maya civilization showed an almost “melted” quality, later ones a crisp outline. This means that we can see this landscape as a palimpsest — that is, like an old parchment manuscript with layers of writing on it, some erased, some added later. The occupational history of a large area is now open to us, pending further testing.
Q: How do the new findings impact the assessment of the stature of the Maya civilization?
Everything is larger, more extensive, more deeply built and engineered than we had thought. In some areas there are denser populations than previously imagined, other regions seem absolutely desolate. And the large-scale fortifications and citadels surely indicate a surprising level of conflict, fear and control. Our few excavations to date suggest that most come from the time of intrusion by an almost imperial power centered on the Mexican city of Teotihuacan, now on the outskirts of Mexico City — for societies that relied on human foot traffic, more rarely canoes, that’s very far away. The defenses we’ve found give some idea of the astonishing impact and scope of militarism of the time.
Q: The LiDAR imagery shows what is under the rainforest — do you know how you and other researchers will address the question of when those structures were built or used?
LiDAR’s immense impact comes from the fact that it pinpoints future directions for research. At one point, I looked at a sector of the LiDAR survey and thought, “there’s a doctoral dissertation, that’s a doctoral dissertation,” and I could have gone on for dozens of other projects. That is the definition of a breakthrough. As I said before, however, looking at a landscape takes you only so far. Now we have to dig. A lot.
Q: What are a few examples of new questions that arise from what the LiDAR shows?
Figuring out what the fortifications were all about is our first task, along with exploring what we now know to be a massive city at El Palmar. The walls and citadels appear to relate to events involving Tikal and Teotihuacan, some of which are mentioned in the glyphic inscriptions I read. At El Palmar, there is an entirely new story to be told. Tikal, taken by scholars to be the main “player” at the time, was in competition with a community at least the same size. What had been a story about one major city is now, with apologies to Dickens, “a tale of two cities.”
Q: What are the implications for the field? Will this change how anthropological and archaeological research is conducted?
The archaeology of ancient tropical urbanism now has two phases, pre-LiDAR and post-LiDAR. This technology transforms everything. It changes how we explore, how we target projects, how we evaluate the cultural patrimony of our host countries, how we study the biotic overlay of trees and vegetation, how we study the soils underneath. Ultimately, it changes how we interpret the achievements of peoples I’ve been studying since I was a teenager. There couldn’t be a more thrilling time for Maya archaeology.