Road to Greener Pastures

The ancient Silk Road waystation Tash Rabat in the Kyrgyzstan mountains lies along a major nomadic pathway for moving herds to high mountain pastures.

Michael Frachetti

The earliest historical records of a network of trade routes across Asia go back to about 200 BCE. Yet, archaeological findings have shown that as early as 2500 BCE, people in the area were trading extensively with each other. Modern-day historians have established the trade routes used in the lowlands by mapping those that were the least costly and easiest to traverse from one major center to the next. At upper elevations, however, data on nomadic activities have shown that “ease of travel” might not have dictated how people moved about and across the mountains. A new study led by archaeologist Michael Frachetti of Washington University demonstrates that the highland pathways traversed by nomadic herders helped to determine the geography of the Silk Road trade routes.

Over the past two decades, Frachetti has spent time living amongst nomadic herders in Kazakhstan, Kyrgyzstan, western China, and other Asian countries. He observed how pastoralists throughout Central Asia seasonally herd their animals out of the grassy lowlands during scorching summers up into cooler, lush mountain meadows during wintertime. Seeing the same pattern wherever he went, Frachetti began wondering how the informal routes might connect to ancient archeological sites such as towns and shrines.

Using a computer model of flow accumulation, which is usually employed to simulate how water in rivers and streams drains throughout a watershed, Frachetti and colleagues entered data on grass productivity obtained through satellite imagery. The model calculated the paths herders were most likely to have taken out of highlands into lowlands by following where grass for their herds was most available. The map covered a roughly 2,500-by-2,500-mile square over the heart of Asia, extending into bordering countries including Iran, India, Russia, and Mongolia.

Having established that model, the researchers then compared its optimal herding corridors to an independently compiled database of Silk Road sites. Amazingly, three-quarters of the Silk Road sites fell along those herders’ well-worn paths. “It was definitely a ‘eureka’ moment,” said Frachetti.

The results not only evidence the rise of the Silk Road’s layout, but hint that some of it remains unexplored. For instance, the model predicts a route into the Tibetan Plateau to the south of the city of Dunhuang in northwestern China.

Contextualizing these findings within the history of Central Asia, Frachetti noted how despite conflicts, cultural differences, and significant geographical obstacles, people still sought ways to connect and participate in each other’s lives. “It’s really an example of where science meets with the human story,” he said. (Nature)