Modern activities follow the contours of ancient Teotihuacan

Lidar mapping study using cutting-edge aerial mapping technology shows the ancient inhabitants of Teotihuacan moved astonishing amounts of soil and bedrock for construction and reshaped the landscape in a way that continues to influence the contours of the modern activities in this part of Mexico. The work is published in the open access journal, PLOS A.

The article also shows how Teotihuacan engineers diverted two rivers to align them with points of astronomical importance, identified hundreds of previously unknown architectural features, and documented more than 200 archaeological features that were destroyed by mining and urbanization since the 1960s.

“We are not living in the past, but we are living with the legacy of past actions. In a monumental city like Teotihuacan, the consequences of these actions are still fresh on the landscape,” said first author Nawa Sugiyama, professor of ‘anthropology. at UC Riverside.

Teotihuacan, about 40 kilometers northeast of present-day Mexico City, was the largest city in the Americas and one of the largest in the ancient world. It existed from around 100 BCE to 550 CE – around 1,000 to 2,000 years ago – and covered 8 square miles. In its heyday, it consisted of numerous pyramids, squares, and well-designed residential and commercial districts with a population of around 100,000. Some of the pyramids and other structures can be seen above ground today, but most of the city’s remains are buried under fields, buildings, and other modern activity areas.

To map the underground parts of Teotihuacan, Nawa Sugiyama and co-authors Saburo Sugiyama of Arizona State University; Tanya Catignani at George Mason University; Adrian SZ Chase at Claremont University; and Juan C. Fernandez-Diaz at the University of Houston used lidar, a mapping technology that measures the time it takes for light from a laser to bounce off an object. Archaeologists often use lidar to uncover buried features covered in dense forests or open fields, but rarely deploy the technology where archaeological remains lie beneath urban areas.

“Lidar is often seen as a revolutionary tool for finding ancient features hidden in plain sight, but we found the lidar map to be extremely complicated and difficult to interpret. Most of the features we identified were modern with ancient roots. a much more interesting story behind this trend, ”said Nawa Sugiyama.

Because the scale of construction in Teotihuacan suggested a massive alteration to the ancient landscape, Sugiyama’s group thought that lidar might help elucidate the relationship between Teotihuacan’s layout and the modern activities that cover it. The researchers confirmed the lidar results with walk surveys and comparisons to previous mapping efforts.

They found that the builders of Teotihuacan leveled the ground down to bedrock and, in some cases, mined the bedrock itself for use as a building and infill material. In just one part of the city, called the Column Square Complex, the authors calculated that about 372,056 square meters of man-made land accumulated over the course of about 300 years of construction that had been mined elsewhere in the Teotihuacan valley. In three of the main pyramid complexes, the authors estimate that 2,423,411 square meters of rock, soil and adobe were used.

This profound overhaul of the landscape affects the arrangement of modern buildings and activities. The authors found that 65% of urban areas contained modern properties or features aligned orthogonally within 3 degrees of 15 degrees east of astronomical north, the same alignment as Teotihuacan. Rock fences were built along areas that lidar and excavation revealed to have ancient underground walls that made modern plowing difficult.

Teotihuacan engineers also diverted the Rio San Juan and the San Lorenzo River, which flow through the city. Rio San Juan follows the orientation of Teotihuacan for 3 km through the city center while the San Lorenzo River has a very distinct orientation, 8 degrees south of the astronomical east for 4.9 km. Previous research has interpreted them as major channels of symbolic and calendar significance.

The lidar map also showed that other sections of canals and rivers, many of which are still actively used today, have been altered at various points along its course, frequently coinciding with the directionalities of Teotihuacan. A total of 16.9 km of hydrologic systems visible in the modern field originate from the Teotihuacan landscape of classical antiquity.

On the lidar map, the group identified 298 features and 5,795 man-made terraces that had not previously been recorded. However, they also identified over 200 known features that have been destroyed by mining since 2015.

“We cannot fight modern urbanization. The lidar map provides a glimpse of these ancient features that are being abolished at an alarming rate that would otherwise go unnoticed. It is one of the many ways we can preserve our heritage landscape “said Nawa Sugiyama.

The authors plan to use their lidar map to create a three-dimensional geospatial database that allows them to visualize stratigraphic and surface data, natural and man-made features, and document the actual extent of humans as geomorphic agents over long periods in Teotihuacan. Valley.

The article “Humans as Geomorphic Agents: Lidar Detection of the Past, Present and Future of the Teotihuacan Valley, Mexico” is published in PLOS ONE.