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Michael Frachetti was on an archaeological dig high in the mountains of southeastern Uzbekistan in 2015 when a forestry official approached him. “You know, I’ve seen some of those kinds of ceramics in my backyard,” the official said, referring to the artifacts emerging from the dirt. “Come see.”
The casual tip would lead Dr. Frachetti, an archaeologist at Washington University in St. Louis, to Tugunbulak, an enormous fortified city dating back to a medieval empire. He and his team would spend nearly a decade trying to map out the site, as well as the one he’d originally come to Uzbekistan to explore, known as Tashbulak.
The results of their research, published on Wednesday in the scientific journal Nature, describe the two sites as “the largest and most comprehensive urban plans of any medieval city” in Central Asia situated at high altitude (defined here as about 6,500 feet above sea level).
“I can’t tell you how exciting this study is,” said Peter Frankopan, a Silk Road expert at the University of Oxford who was not involved in the study.
The findings complicate the prevailing image of the Silk Road, which facilitated the exchange of goods and ideas between people from China to Venice between the second century B.C. and the 15th century A.D. Many experts had previously thought that the famous trade route passed only through the lowlands.
But in fact, “they were dragging the caravans to the mountains,” said Farhod Maksudov, an archaeologist at the Uzbekistan Academy of Sciences. Because the surrounding Malguzar Mountains were rich in iron ore, Tashbulak and Tugunbulak may have been centers of weapons manufacturing. Dr. Maksudov said that excavations at the two mountain sites had yielded pottery, coins and jewelry, which may have been traded for weapons and other objects.
“These sites hint at the significance of ores and metals,” Dr. Frankopan said.
The willingness of medieval merchants to detour up the mountains suggests a complexity of trade routes absent from popular conceptions of the Silk Road. “Stereotypically, we think that it’s like a highway,” Dr. Maksudov said. “No — it’s very highly networked.”
Initiated by the Chinese explorer Zhang Qian, who went in search of “heavenly horses” for the Han dynasty, the Silk Road eventually connected people living thousands of miles apart, in ways both predictable and not.
Because of their position between East and West Asia, the Central Asian cities of Samarkand and Bukhara served as important Silk Road hubs. Much later, they became cities in the Soviet republic of Uzbekistan. Dr. Maksudov explained that the U.S.S.R. imposed a Marxist version of history on the region, celebrating large urban developments while downplaying the contributions of medieval nomadic peoples, like those who possibly settled Tashbulak and Tugunbulak.
“Scholars used to think about nomadic and sedentary societies as separate and distinct,” Dr. Frankopan said. “These sites show clearly that reality was much more complicated, with mobile communities not only creating settlements but large ones, too.”
When Dr. Frachetti arrived in Uzbekistan in 2010, the high plateau where Tashbulak and Tugunbulak had been situated had long reverted into “grassy, undulating fields with large, pyramidical mounds,” the new paper noted.
Still, Tugunbulak, an area of 390 acres, proved difficult to study because of its sprawling size. Uzbekistan has strict rules against drones, making the most obvious means of exploring the sites potentially unfeasible. Drs. Frachetti and Maksudov worked for months with officials at the Uzbek embassy in Washington, D.C., to secure permission for aerial surveys.
“It’s very difficult to bring equipment into Uzbekistan,” said Zach Silvia, an archaeologist at Brown University. “It’s quite the feat that he’s able to do this work.”
Still, there were challenges. High winds blew one drone away. And many of the images that drones did capture were “subpar,” Dr. Frachetti said. Exploring a site as large as Tugunbulak with ground-penetrating radar was unrealistic in those initial stages of the project.
In 2022, Dr. Frachetti returned to Uzbekistan with a high-end drone outfitted with a lidar camera. Lidar, which stands for “light detection and ranging,” creates topographical images by measuring how long it takes a laser beam to travel between the camera and a surface. Attaching the camera to a drone allowed Dr. Frachetti to explore difficult-to-access mountain sites. He and his team conducted one flight over Tashbulak, capturing 43 million surface data points. Tugunbulak required 22 flights, netting 421 million data points.
The lidar images were superior to standard drone photography but still lacked clarity in places. Dr. Frachetti turned to his Washington University colleague Tao Ju, a computer scientist who used a custom algorithm to parse the lidar data, ultimately finding evidence of walls, roads and buildings.
Just a small fraction of Tugunbulak has been unearthed, work that no algorithm can do.
“You really don’t fully understand what you’re dealing with until you just go back to the old methods,” Dr. Silvia said. “You go back to the spade at the end of the day.”
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