Seasonal migrations marked early steps in establishing cross-continental trade route
Nomadic herders took the ancient Silk Road to new heights.
Starting 4,000 years ago or more, Central Asian herders routinely migrated from highland pastures in summer to lowland areas in winter (SN: 5/3/14, p. 15). Over roughly the next 2,000 years, those routes through mountainous regions eventually became a key part of the Silk Road, an ancient trade and travel network stretching from China to Europe, says a team led by anthropologist Michael Frachetti of Washington University in St. Louis.
This finding underscores the important contribution of nomadic herders, interacting with lowland farmers and early city dwellers, to the Silk Road and overland trade, the researchers conclude in the March 9 Nature. Extensive Silk Road pathways ran across Asia by around 2,200 years ago. Merchants, pilgrims, monks and soldiers, as well as nomads, traveled these routes (SN Online: 7/29/16).
Contrary to the traditional view of nomadic groups as barbarians, the new paper supports a growing conviction among researchers that mobile herders contributed to the rise of early states and civilizations, says Yale University archaeologist William Honeychurch.
Frachetti agrees. In a mountainous part of Central Asia without cities — an area stretching from what’s now western China to Afghanistan and Pakistan — highland routes made it possible for travelers from many eastern and western lowland centers to journey across the continent. Contacts among highland herders and lowland populations eventually resulted in cradles of civilization in China and elsewhere, Frachetti suspects. “Silk Road highland networks were formed by pastoralists interacting with other groups in a lengthy process that was not a construction project and involved no planning,” he says.
Because travel routes out of the mountains varied from year to year depending on locations of productive grasslands, herders didn’t always beat clear-cut paths into the turf. But Frachetti suspects that, like recent nomadic groups, ancient herders built stone structures and other landmarks that served as travel guides and provided directions to outsiders venturing through Central Asia’s lofty mountains.
Using satellite imagery and geographic mapping software, Frachetti’s group created 500 computer simulations of nomadic herders’ seasonal descent routes from highland locations situated between 750 and 4,000 meters above sea level. These simulations represented 500 years of seasonal treks from highland to lowland camps.
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Simulations favored routes with the best pastureland for grazing animals from one year to the next, based on modern measures of vegetation and climate fluctuation in Central Asia. Those measures are similar to what’s known about conditions in Central Asia several thousand years ago, Frachetti says.
His team mathematically folded all 500 simulations into a cumulative route. A small number of descent paths that frequently popped up in individual simulations largely shaped the cumulative route, Frachetti says. That route intersected with 192 of 258 Silk Road archaeological sites that have been discovered at high altitudes, after allowing for a leeway of two kilometers from the simulated route. The team reasoned that, since simulated routes often ran through grassy pastures, travelers’ inns and other structures were probably built nearby.
Some highland sites lying outside the cumulative route were still within a few kilometers of it. Computer simulations didn’t pick up sites that were located on occasionally traveled paths, between especially high mountain peaks, for instance, Frachetti says.
Nomads’ contributions to the Silk Road need to be explored further by looking for more highland sites that map onto ancient herders’ simulated travel routes, Honeychurch says. Herding groups trekked in certain directions to avoid dangers and for many other reasons, not just to find pastures and water, he cautions.
M.D. Frachetti et al. Nomadic ecology shaped the highland geography of Asia’s Silk Roads. Nature. Vol. 543, March 9, 2017, p. 193. doi:10.1038/nature21696.
B. Bower. Parasitic worm eggs found on Silk Road latrine artifacts. Science News Online, July 29, 2016.
B. Bower. Bronze Age herders spread farming around Asia. Science News. Vol. 185, May 3, 2014, p. 15.