The Silk Road was a series of ancient trade routes that once connected China to the Roman Empire. Research published in the journal Nature reported the discovery of two fortified cities—Tashbulak and Tugunbulak—in the mountains of southeastern Uzbekistan, 7,000 feet above sea level. Urban centers above 6,000 feet are rare.

The discovery is important because it had been assumed that ancient trade routes avoided the mountains of Central Asia. Archaeologists used light detection and ranging equipment (LiDAR), a drone mapping technology, to create a detailed map of these large urban centers, which included watchtowers, fortresses, complex buildings and plazas.