Silk Road cities reached surprising heights in Central Asia’s mountains

Two high-altitude, medieval cities built by mobile herders along Silk Road trade routes in Central Asia have been hiding in plain sight — until now.

Mountainous regions typically have been seen as obstacles to trade and communication. But these ancient settlements, located roughly 2,000 meters above sea level, show that herding communities developed a distinctive form of urban life where such activities thrived, archaeologist Michael Frachetti and colleagues report October 23 in Nature.

“Think of these high-altitude cities as nodes in a network that moved power and trade through Asia and Europe,” says Frachetti, of Washington University in St. Louis.

Researchers have discovered buildings and cultural items from only a few ancient settlements located more than 2,000 meters above sea level, such as Peru’s Machu Picchu. Despite thin air, a harsh climate, rugged terrain and limited farmland, it now appears that mountainous Central Asia was “an urban zone” during medieval times, Frachetti says.

The team focused on two archaeological sites in southeastern Uzbekistan: Tashbulak and Tugunbulak. Centuries of erosion and sediment buildup have obscured the urban features of both sites, located five kilometers apart, beneath undulating grasslands. Large earthen mounds and pottery pieces scattered on the landscape led to the discovery of Tashbulak in 2011 and Tugunbulak in 2015. Those finds indicate that Tugunbulak was occupied from the 6th to 10th centuries. Initial residents of Tashbulak arrived in the 8th century.

Using drones mounted with light detection and ranging, or lidar, technology, Frachetti and colleagues mapped the extent and layout of both sites. Lidar’s laser scans have previously peered through tropical jungles and ground cover to reveal ancient urban networks in the Amazon, Central America and Cambodia (SN: 1/11/24; SN: 12/4/23; SN: 4/29/16).

Lidar maps of surface-level ridges in the soil where walls once stood, augmented by computer reconstructions of those buildings, indicate that Tugunbulak covered just over a square kilometer. It stood as one of the largest Central Asian cities of its time, Frachetti says.

The more than 300 structures at Tugunbulak included clusters of buildings with shared walls, narrow corridors or roads running between those clusters, watchtowers connected by walls along a ridgeline and a central fortress or citadel.

Tugunbulak’s layout mirrored that of small and large lowland cities in medieval Asia, the researchers say. The mountain city’s fortress, flanked by a castle or palace, overlooked a town surrounded by defensive walls.

Tashbulak covered roughly one-eighth the territory of Tugunbulak but was still a bustling community, Frachetti says. A string of large defensive structures overlooked a vast area of terraced platforms, walls and houses. At least 98 structures identified so far resemble the types of buildings detected at the larger site, the researchers say.

Population sizes are difficult to estimate for the two communities. But Frachetti suspects that a relatively constant number of year-round residents increased periodically during gatherings for special events and exchanges of goods.

Lidar’s unveiling of large communities at Tugunbulak and Tashbulak highlights the unappreciated ability of high-altitude herding groups to band together as early city builders, says archaeologist Michael Fisher of the Max Planck Institute of Geoanthropology in Jena, Germany. The new study demonstrates that “mountain ranges can actually be conduits for cultural and economic transmission, not barriers.”

Mountain ranges present little opportunity for farming, however, raising questions about how Tugunbulak and Tashbulak populations were fed.

Highland pastures supported herds of cattle, sheep, goats and horses that could have been traded or sold to obtain cultivated foods. Previous excavations at Tashbulak uncovered remains of grains, legumes, nut shells, fruits, chicken eggshell fragments and cotton seeds. Regular shipments of these foods must have come from lowland settlements, says Max Planck archaeologist Robert Spengler, who participated in those earlier digs.

Excavations conducted since 2022 suggest that large-scale iron production occurred at Tugunbulak and Tashbulak, Frachetti says. Iron represented a valuable trade item for highland city dwellers.

These mountain cities may have also provided rest stops for caravans traveling the Silk Road, a set of ancient trade and travel routes that ran from China to Europe. But excavations have yet to confirm that possibility.