A name invented long after the fact

No merchant in the year 700 ever said he was traveling the Silk Road. The phrase was coined by a German geographer in the nineteenth century, and it stuck because it is vivid. Most historians now write of the Silk Roads, in the plural, because there was never a single paved highway. There was a shifting tangle of tracks, passes, river crossings and sea lanes that linked China, Central Asia, India, Iran and the Mediterranean for roughly two thousand years. Silk was the most famous thing carried along them, but it was one good among hundreds, and ideas, religions, languages and diseases traveled the same paths.

The lay of the land

Start in the Chinese heartland along the Yellow River. Travelers heading west entered the Hexi Corridor, a strip of oases between mountains and desert: the snowy Qilian range on one side and the Gobi on the other, in what is now Gansu province. At the corridor's western end stood the garrison town of Dunhuang, the last stop before real wilderness.

Beyond Dunhuang lay the Tarim Basin and, filling most of it, the Taklamakan Desert, a sea of shifting dunes so dry that travelers dreaded it. Caravans did not try to cross the middle. Instead the routes split. A northern route ran along the foot of the Tian Shan mountains through oases such as Turfan and Kucha. A southern route ran along the Kunlun mountains through Khotan, famous for its jade. The two branches met again at Kashgar, at the basin's western edge.

From Kashgar the way west climbed into the Pamirs, a knot of mountains so high that locals called the region the Roof of the World. Past the passes lay the fertile Ferghana Valley, then Sogdiana with its cities of Samarkand and Bukhara, then Bactria (northern Afghanistan), the Iranian plateau, Mesopotamia and finally the ports of Syria. A steppe route ran across the grasslands to the north, and sea routes crossed the Indian Ocean.

Oases and camels

Overland trade was possible only because of oases, fed by rivers of snowmelt running down from the mountains and then vanishing into the sand. Each oasis could support a city, irrigated fields and a small kingdom, and each kingdom earned money by feeding, housing and taxing the people passing through. Khotan, Kucha and Turfan had their own languages, rulers and art.

The workhorse of the desert was not a horse. It was the two humped Bactrian camel, which could carry a heavy load for days, go long stretches without water and, crucially, endure both bitter cold and dry desert. Winters in the Tarim Basin are freezing, so the one humped dromedary of Arabia was less suited. In the high passes, yaks and sure footed ponies took over.

Relay trade, not marathon journeys

Very few people or goods went the whole distance. Most trade worked as relay trade, in which goods passed from merchant to merchant in stages. A trader from Kucha might carry cloth to Kashgar and sell it there; a Sogdian might carry it on to Samarkand; a Persian might take it further west. Each sale added a margin, so prices climbed with distance. The people who did cover great distances were mostly envoys, pilgrims and missionaries.

How big was the trade?

Historians disagree about the scale. Valerie Hansen, in a much discussed history published in 2012, studied documents found in the desert and argued that overland traffic was mostly local and modest in volume. Caravans were often small, many transactions were between neighbors, and much of the money in the region came from the Chinese state paying its frontier garrisons.

Others answer that volume is the wrong measure. Silk, gems and spices packed great value into little space, so a few camel loads could be worth a fortune. More important, small numbers of travelers still carried ideas, faiths and germs that changed whole civilizations. Both points can be true: the Silk Roads were less like a modern freight corridor and more like a slow, branching nervous system for Eurasia.

Worked example: following one bolt of silk

Picture a bolt of plain silk woven near the Tang capital, Chang'an, around 700. The government collects it as tax and ships it west to pay soldiers at a garrison near Turfan. A soldier spends it at the local market, where a Sogdian trader accepts it in exchange for a horse. The trader takes it over the Pamirs to Samarkand and sells it to a merchant bound for Iran. Years later, the same cloth ends up wrapping a saint's relic in a church in the Byzantine world, where no one has heard of Turfan.

Trace the steps and the lessons of this level appear. No one carried the silk end to end; it moved in relays. It served as tax, wages and money before it ever became a luxury. The route ran through oases with their own economies, and much of the motion came from the state paying its army, which supports Hansen's view. Yet the cloth still linked people who would never meet, which supports her critics. Asking "Who handled this, and why?" is the habit this course builds.