Lost Silk Road cities mapped using remote sensing

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Lost for centuries, two cities lay buried, nearly 5 kilometers (3 miles) apart, underneath grassy pastures in the mountains of Uzbekistan. Now, archaeologists for the first time have mapped these intriguing highland strongholds in the country’s southeast — once a key crossroad of ancient silk trade routes — that were inexplicably abandoned.

Using drone-borne LiDAR — light detection and ranging equipment — that can find structures obscured by vegetation, researchers captured images revealing two unexpectedly large-scale urban settlements dotted with watchtowers, fortresses, complex buildings, plazas and pathways that tens of thousands of people may have called home.

Uncovering what would have been bustling medieval cities at a dizzying elevation of more than 2,000 meters (6,562 feet) above sea level was surprising, said anthropologist Michael Frachetti, lead author of the new research published Wednesday in the journal Nature.

Life in the two settlements would have been tough, particularly during the winter months. “This is the land of nomads, the land of pastoralists. It’s a periphery as far as most people are concerned,” said Frachetti, a professor of archaeology at the Spatial Analysis, Interpretation and Exploration laboratory at Washington University in St. Louis.

Today, only 3% of the planet’s population lives at or above such great heights, mainly on the Tibetan Plateau and in the Andes, according to the study. Ancient highland settlements, such as Machu Picchu in Peru, are considered anomalies given the harshness of life at high elevations, the study noted.

“It’s a really different environment up there,” Frachetti said of the newly discovered Silk Road settlements. “It’s winter there already. It’s freezing cold. We get snow in summer.”

The archaeological team has kicked off preliminary excavations at the two sites to unravel who exactly established the enigmatic lost cities — and why.

High mountain cities of nomads?

Central Asia’s mountains and steppes have been home to powerful nomadic groups for thousands of years. These nomads on horseback built empires, centering their lives around herding animals such as sheep, goats and cattle since the Bronze Age.

However, the newfound highland cities were too big to simply be trading posts or Silk Road stopovers, Frachetti and his colleagues believe. More likely, they reasoned in the study, the urban settlements were built to exploit abundant iron ore found underground in the region. The team hopes excavations will reveal who founded and lived in the cities.

“The entire region is sitting on a highly prized commodity of the time, which is iron, and it’s also dense in juniper forest, which would have provided fuel (for smelting),” Frachetti said.

While the region isn’t suitable for agriculture, he thinks the surrounding land would have sustained the cities’ inhabitants by supporting grazing herds as part of the pastoral lifestyle that had long existed there. Moreover, the mountain terrain would have also offered an effective defensive position.

Along with his Uzbek colleague and study coauthor Farhod Maksudov, a researcher and director at the National Center of Archeology at the Academy of Sciences of the Republic of Uzbekistan, Frachetti first came across one of the settlements in 2011 while conducting an archaeological survey of the region.

“Our goal at that time was really to study the prehistory of these mountain regions as it relates to the development of nomadic pastoralism,” he said.

“In the process of that work, we stumbled upon the smaller of the two cities, Tashbulak, and it was quite a sensation to find a highland city,” he said.

Laser mapping reveals archaeological wonders

Frachetti and his colleagues found the second and larger of the two cities, Tugunbulak, in 2015 after a local forestry worker mentioned similar shapes to those in Tashbulak in the landscape where he lived.

“We got down there and right in his backyard is a medieval citadel. He just didn’t know it.
We go up to the mound and we look out, and we can see mounds and pyramidical (shapes) all over the place, and we’re like, oh my gosh, this place is huge.”

The team mapped the two cities in 2022, making 22 flights with a drone equipped with LiDAR. The endeavor marked the first time researchers have used the technology in the region, according to the study.

A LiDAR sensor tracks the amount of time each laser pulse takes to return and uses that information to create a three-dimensional map of the environment below. The technique has revolutionized the study of human history and culture and been particularly useful in discovering archaeological sites in the Amazon rainforest and Maya sites in Central America.

During the heyday of the medieval Silk Roads, cities emerged and other flourished, said Zachary Silvia, a postdoctoral research associate at the Joukowsky Institute for Archaeology and the Ancient World at Brown University in Rhode Island. But better known towns along the route such as Samarkand in Uzbekistan and Kashgar in China, were situated in vast agricultural oases.

“High-altitude urban sites are extraordinarily rare in the archaeological record because of a unique set of landscape challenges and technological demands that must be overcome for people to form large communities in mountainous areas,” Silvia, who was not involved in the research, wrote in a commentary that was published alongside the research.

“The discovery of Tashbulak and Tugunbulak forces us to reconsider notions about the optimal location for establishing a city.”

The study, based on the LiDAR data, found that Tugunbulak occupied approximately 1.2 square kilometers (120 hectares) and showed evidence of more than 300 unique structures, which vary in size from 30 to 4,300 square meters (323 to 46,285 square feet).

Tashbulak, meanwhile, covered 0.12 to 0.15 square kilometers (12 to 15 hectares) and while smaller, included a citadel made of an elevated mound surrounded by dense architecture and walled fortifications made from packed earth. The study team found at least 98 visible habitations, which shared a similar shape and size to those in Tugunbulak.

The researchers believe Tashbulak was inhabited between the sixth and 11th centuries, while Tugunbulak was active from the eighth to 11th centuries, he said.

It’s not clear why the settlements were abandoned. “Those stories will become clearer once we delve deeper into the archaeology,” Frachetti said. There is no sign that they were razed, burned or attacked, he added, but it’s a topic of active study.

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