Trade was the engine that kept the Silk Road turning. Understanding what moved, and how, reveals a commercial world far more intricate than a single stream of silk heading west.
What moved
Chinese silk travelled west, light and precious; so, in time, did paper, whose manufacture was a closely guarded secret. Coming the other way and criss-crossing the middle were spices and incense, glass from Rome and the Levant, gems and jade, wool and furs, and above all horses: the tall, strong "heavenly horses" of Central Asia that Chinese emperors craved for their armies. Ideas and seeds moved too: grapes, walnuts, and new crops spread along with the cargo.
The middlemen
Very little of this was carried end to end. The trade ran on middlemen, merchants who worked a familiar stretch and sold on to the next link in the chain. The Sogdians, an Iranian people from around Samarkand, became the great brokers of the eastern routes, their language a common tongue of trade for centuries. Each exchange added a margin, which is why a commodity cheap at its source became a luxury by the time it reached the far end.
The caravans and their inns
Goods travelled by caravan: long trains of camels, the desert's ideal freighter, able to carry heavy loads for days between water. Camels set the rhythm of the whole enterprise: the distance between stops, the size of a load, the pace of a journey.
Sheltering them was the caravanserai, a fortified roadside inn built around a large courtyard, spaced roughly a day's march apart. There merchants and animals could rest safely for the night, stable their beasts, store their goods, and meet traders coming the other way. The caravanserais were not just shelter but marketplaces and clearing-houses of news, where prices, routes, and rumours were traded as busily as silk.