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T
he Silk Road — the ancient
trade route that stretched
thousands of kilometers
from China to the Mediter-
ranean — often calls to mind images of
large camel caravans trekking for months
across deserts and over mountains, car-
rying luxurious linens, spices and gems
between distant lands. In reality, the
“road” comprised a network of many
shorter relays between neighboring areas,
with goods often changing hands many
times in cities, rural villages and even
remote trading outposts. The webbed
nature of the network has long com-
plicated archaeological efforts to map
exactly where and how the Silk Road
developed. In a recent study in Nature,
researchers have illuminated likely routes
of Silk Road travelers through a region of
particularly challenging terrain — moun-
tainous Central Asia — with the help of
an innovative mapping method.
The scientists who conducted the
study, which compared sophisticatedmapping of high-altitude
grasslands in Central Asia and
satellite imagery to the locations
of known Silk Road trading
stops, posit that mountainous
stretches of the road may have
been paved by the stamping
feet of goats, sheep and their
nomadic herders for centuries
before exotic luxuries were
ever hauled over them. “Just
like big cities, small herding
villages during this era under-
stood that regional trade was a
way to increase quality of life
and economic standing,” says
Michael Frachetti, an archaeol-
ogist at Washington University
in St. Louis and lead author of
the study. “These people didn’t see these
mountains as obstacles; traversing them
was a normal part of life.”
For several thousand years, nomadic
herders, or pastoralists, in Central Asia
have migrated their herds to higher ele-
vation grasslands during the hot, dry
summer months to access more, and bet-
ter, forage for their animals. Frachetti
and his fellow researchers used satellite
imagery and geographic information sys-
tem (GIS) mapping tools typically used
to model streamflows based on gravity
and topography. But instead of streams,
they modeled seasonal fluctuations and
patterns in the quantity and quality of
highland grasses. Based on grassland loca-
tions, they predicted the likely routes that
ancient herders would have used each
year to traverse the mountains in parts of
present-day Afghanistan, China, Kazakh-
stan, Kyrgyzstan, Pakistan, Tajikistan,
Uzbekistan and elsewhere.
After 500 unique model simulations,
each representing one year, likely routes
became pronounced, establishing a
web of trails and roads. These routes
were then compared to the locations of
258 sites associated with the Silk Road
and within the altitude range of these
highland grasslands. With the datasets
overlaid, the researchers found that theroutes likely to have been used most
by herders connected 74 percent of
the known Silk Road locations. “This
correlation suggests this vast network
of regional connectivity was signifi-
cantly influenced, and even somewhat
established, by these small mountain
communities,” Frachetti says.
He and his colleagues noted several
reasons why following the pastoralists
would have made sense for Silk Road
traders. Local pastoralists tend to have
an intimate knowledge of safe routes
through mountains and how these
routes can change seasonally. Also, they
would’ve naturally moved between out-
posts to keep themselves and their flocks
supplied with necessities like water, and
for protection from predators. “Sections
of these mountains can be incredibly
barren, making these small outposts
essential infrastructure for passage,”
Frachetti says.
Another reason is that “there’s a
strong relationship between topogra-
phy and grassland,” says Joshua Wright,
an archaeologist from the University
of Aberdeen in Scotland who wasn’t
involved with the study. “Grass is only
going to grow in flatter areas of the
mountains — the flatter the terrain, the
easier it is to travel and build outposts,”&LIVHIVPIEHWWLIITXLVSYKLQSYRXEMRSYWXIVVEMRMR
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