Satellite and lidar images of the Sun Pyramid at Teotihuacan. The satellite portion of the image is in the left-hand half, while the lidar portion shows buried walls and other archaeological features. Credit: Nawa Sugiyama
An aerial mapping technology that uses lidar to map the area shows how ancient inhabitants of Teotihuacan shifted large amounts of soil and rock for construction. This reshaped the landscape and continues to shape the course of modern activity in this region of Mexico. The paper is published in the PLOS One open-access journal.
This paper also shows how Teotihuacan engineers re-routed rivers to align with points astronomical in significance. It also identifies hundreds of previously undiscovered architectural features. The paper also documents over 200 archaeological features that were destroyed by urbanization and mining since the 1960s.
"We don’t live in the past. But we live with the legacy of past actions." The consequences of past actions still have a fresh impact on a city as monumental as Teotihuacan," stated Nawa Sugiyama (UC Riverside professor of anthropology).
Teotihuacan was located 25 miles northeast from modern Mexico City. It was the largest American city and the largest in ancient history. It occupied 8 square miles and was in existence between 100 BCE and 550 CE, approximately 1,000-2,000 years ago. It was home to around 100,000 people at its peak, with numerous plazas and pyramids. While some of the structures can still be seen above ground, most of the remains of the city are buried under modern buildings and fields.
Nawa Sugiyama, Tanya Catignani at George Mason University, Adrian S. Z. and Saburo Sugiyama from Arizona State University mapped the below-ground areas of Teotihuacan. Chase at Claremont University, Juan C. Fernandez Diaz at Houston University, and Nawa Sugiyama at Arizona State University, Tanya Catignani at George Mason University, and Adrian S. Z. used lidar. This is a technology that measures how long it takes for light from a laser beam to bounce back from an object. Although archaeologists use lidar often to find hidden features in dense forests and open fields, they rarely use the technology for archaeological remains beneath urban areas.
Although lidar is often viewed as a revolutionary tool for finding ancient features hidden in plain view, we found the lidar maps to be very messy and difficult to understand. Many of the features that we found were modern, but had ancient roots. We realized that there was a much more interesting story behind the trend," stated Nawa Sugiyama.
Sugiyama's group believed that lidar could be used to help explain the relationship between Teotihuacan's layout and the modern activities that are layered on top of it. This was due to the scale of Teotihuacan's construction. With surveys done on foot, the researchers confirmed their findings and made comparisons with previous mapping efforts.
The researchers discovered that Teotihuacan's builders had lowered the ground to the rock and quarried some of the rock to be used as fill material and construction materials. The Plaza of the Columns Complex is the only part of the city that the authors have calculated to contain approximately 372,056 square metres of artificial ground. This was a result of nearly 300 years of construction and material quarried from other parts of the Teotihuacan Valley. The authors estimate that 2,423,411 sq. meters of dirt, rock, and adobe were used in three of the main pyramid structures.
This significant reshaping affects the arrangement and activities of modern construction. According to the authors, 65% of urban areas had property or modern features that were orthogonal within 3 degrees of 15 degree east of astronomical North. This is the same alignment as Teotihuacan. Rock fences were constructed along areas where excavation and lidar revealed ancient walls that made modern-day plowing difficult.
Teotihuacan engineers also changed the route of the Rio San Juan, and San Lorenzo Rivers that cross the city. The Teotihuacan orientation of Rio San Juan runs for 3km through the city center, while the orientation of the San Lorenzo River for 4.9km is very different. It follows 8 degrees south from the astronomical east. They were previously identified as major canals with symbolic and calendric importance.
A lidar map showed that many other sections of rivers and canals, many of which are still active today, were also altered along their course. These changes often coincided with the Teotihuacan directions. The Early Classic Teotihuacan landscape was responsible for 16.9 km of all the hydrological systems that are visible today.
The group found 298 features and 5,795 terraces created by humans on the lidar map. These were not previously documented. They also identified more than 200 features that were destroyed by mining in the past five years.
"We can't fight modern urbanization. This lidar map shows us a glimpse of the ancient features being lost at a rate that is alarming. It is one of many ways that we can preserve our heritage landscape," stated Nawa Sugiyama.
They plan to use the lidar map to create three-dimensional geospatial databases that allow them to visualize stratigraphic, surface, and natural features. This will also help them document the true extent to which humans have been acting as geomorphic agents for long periods in the Teotihuacan Valley.
PLOS ONE published the paper "Humans as Geomorphic Agents: Lidar detections of the past, present, and future of Teotihuacan Val, Mexico"
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More information: Nawa Sugyama et., Humans as Geomorphic Agents: Lidar detections of the past, present, and future of Teotihuacan, Mexico, PLOS One (2021). Information from the Journal: PLoS ONE Nawa Sugyama et. al. Humans as geomorphic Agents: Lidar detections of the past, present, and future of Teotihuacan, Mexico (2021). DOI: 10.1371/journal.pone.0257550
