CSU researcher uses drone-based lidar technology to uncover ancient cities

Contact for reporters:

Stacy Nick
[email protected]

Colorado State University Associate Professor Edward Henry is available for interviews on the use of drone-based lidar technology to uncover ancient cities in Central Asia and St. Louis, Missouri, as well as what these discoveries can teach us about urbanism today.

 

The first-ever use of cutting-edge drone-based lidar in Central Asia allowed archaeologists to capture stunning details of two newly documented trade cities — Tashbulak and Tugunbulak — high in the mountains of Uzbekistan.

A team of researchers — including CSU Associate Professor of Anthropology and Geography Edward Henry and led by Washington University in St. Louis Professor of Anthropology Michael Frachetti and Farhod Maksudov, director of the National Center of Archaeology in Uzbekistan — used drone-based lidar to map the archaeological scale and layout of two recently discovered high-elevation sites in Uzbekistan. The medieval cities are among the largest ever documented in the mountainous parts of the Silk Road, the vast network of ancient trade routes that connected Europe and Eastern Asia.

The tip of the iceberg

When the team first began collecting data on Tashbulak in 2013, Henry said they were excited to find interconnected systems of architecture, as well as a necropolis through geophysical surveys.

“Then, while collecting GPR data in 2015, we found Tugunbulak,” he said. “That was the moment where we really took a step back and realized that we weren’t just dealing with one ‘small mountain town.’ We weren’t dealing with Vail; we were dealing with the I-70 corridor.”

The use of ground-penetrating radar and drone-based lidar scans provided detailed views of the buildings, plazas, fortifications, roads and habitations that shaped the lives and economies of highland communities, traders and travelers from the sixth through 11th centuries in Central Asia. The cities are located in rugged terrain 2,000 to 2,200 meters above sea level — roughly comparable to Machu Picchu in Peru — making them unusual examples of thriving mountain urbanism.

Among some of the finds indicating trading beyond iron and sheep or goat herds were remnants of common lowland vegetables and fruits, including peaches.

“It’s an interesting look at the importance of these highland settlements in the ways they interface with lowland oases and urban settlements,” Henry said. “They’re not these cultural backwaters or rural areas in the sense that I think most people conceive of.”

The centimeter-level scans allowed for advanced computer analysis of the ancient archaeological surfaces, providing an unprecedented view of the cities’ architecture and organization.

“These are some of the highest resolution lidar images of archeological sites ever published,” Frachetti said. “They were made possible, in part, because of the unique erosion dynamics in this mountain setting.”

The smaller city, Tashbulak, covered about 12 hectares, while the larger city of Tugunbulak reached 120 hectares, making it one of the largest regional cities of its time, he noted.

“This site had an elaborate urban structure with specific material culture that greatly varied from the lowland sedentary culture,” Maksudov added. “It’s clear that the people inhabiting Tugunbulak for more than a thousand years ago were nomadic pastoralists who maintained their own distinct, independent culture and political economy.”

Lidar technology is commonly used to map archaeological landscapes blocked by dense vegetation, but it has additional value where vegetation is sparse, such as the mountains of Uzbekistan.

The high elevation proved a challenge for the team, along with extreme weather shifts. In addition, the site was in a militarized zone where drone operation was strictly regulated, requiring a long permitting process and scrutiny over each and every piece of equipment.

High-tech archaeology

The team first discovered the highland cities using predictive computer models and old-fashioned foot surveys between 2011 and 2015, tracing presumed routes of the Silk Road in southeastern Uzbekistan. The project took years to materialize. The extra time ultimately proved to be a blessing, allowing the researchers to make the most of the latest advances in drone-based lidar.

“The final high-res maps were a composite of more than 17 drone flights over three weeks,” Frachetti said. “It would have taken us a decade to map such large sites manually.”

The team compiled the drone-lidar data into 3D models and then applied computational algorithms to analyze the archaeological surfaces and auto-trace millions of lines to predict likely architectural alignments. The final step was to match the digital output with comparable architectural cases, revealing a huge ancient city otherwise invisible to the naked eye.

“Our ability to validate and critique the automated feature detection from the lidar surface was made possible by the existence of detailed GPR data at Tashbulak — essentially providing us with a subsurface ‘Rosetta Stone’ to connect real architectural remains with their topographic signature” Frachetti said.

It’s already clear that Tashbulak and Tugunbulak weren’t just remote outposts or rest stops, but part of serious geopolitical entities where critical resources were being traded.

Both cities warrant much closer inspection, Frachetti said. Preliminary digging at one of the fortified structures at Tugunbulak suggests that the fortress — a building protected by 3-meter-thick rammed earth walls — might have been a factory where local metalsmiths turned rich deposits of iron ore into steel. Such industry would have been a key feature of the city and its economy.

“When people initially studied the Silk Road, they looked at a lot of the lowland caravan routes and didn’t appreciate the fact that people were also taking those caravans into the mountains as well,” Henry said. “There is a common misconception that people living during the development and expansion of the Silk Road only took the easiest route instead of maybe taking the road less traveled, so to speak. With the discovery of Tashbulak and Tugunbulak, this idea that people would not want to expend the energy or the resources to go into the mountains is starting to fall apart.”

Keys to our future

Next steps will likely involve more traditional on-the-ground archaeology, along with additional drone-based lidar to help understand more about what the two cities’ layouts mean in terms of urban planning, where the administrative and bureaucratic elites lived versus trades people, as well as the distribution of social hierarchy. These will be key to understanding the larger questions of these urban settlements.

The iron ore extraction and processing that went on there takes a lot of heat, requiring high-temperature fires, Henry said. If people were cutting down many of the native Juniper trees on this landscape to build those fires, that would have led to significant levels of erosion.

“Was there a level of environmental degradation that occurred that no longer made a highland urban settlement sustainable?” he asked. “How does that happen, and when or how quickly does that happen? These are the kinds of questions that lead us to wonder how these cities ultimately failed. We have a little bit of an understanding now that there were cities there and that they were very successful, but were they sustainable and if so, for how long? And if not, why?”

The answers to these questions could have implications for society today, said Henry, noting the similarity to another project that he is leading on the city of Cahokia, near present-day St. Louis, Missouri, which looks at how Native Americans in that region engaged in urbanism.

“Right now, the UN is reporting that about 55% of the world’s human population live in cities, and they project that to increase to 68% by 2050,” he said. “So, if this is the kind of path that humans are on, I think it speaks to the importance of understanding how we became attracted to living in cities, how that rural-to-urban transition is happening, and what are the differences in how this process unfolds around the world and through time. It’s all part of that larger human history we share as global citizens.”