In 138 BCE Han emperor Wu dispatched Zhang Qian westward to seek allies against the Xiongnu nomads. Captured by the Xiongnu on the way, Zhang spent more than a decade in captivity before escaping and reaching Ferghana, Bactria and Sogdiana. When he returned to Chang'an in 126 BCE the political result was modest, but his detailed reports on the agriculture, cities, markets and Hellenistic influences he had seen mapped an unknown world for the Han court.

In the following decades the Han state established garrisons along the Tarim Basin that made the route reasonably safe. What emerged was not a single 'road' but a network of desert oases, mountain passes and steppe corridors along which caravans moved goods in short relays. Silk, lacquerware and later paper went west from China; glass, wool, grapevines, alfalfa, silver and above all the 'heavenly horses' of Ferghana came east. Sogdian and Bactrian merchants did most of the carrying.

The goods mattered, but the culture they carried mattered more. Buddhism spread through the Kushan Empire into the Tarim oases and on to China; Hellenistic sculptural conventions shaped the very first images of the Buddha in Gandhara. Knowledge of metallurgy and silk production seeped westward over centuries. The Han, Parthian, Kushan and Roman worlds now knew of each other's existence — even without meeting directly.

The term Silk Road is itself modern (coined by Ferdinand von Richthofen in 1877). It was never a single state-built infrastructure but a long-running pattern of exchange. Even so, Zhang Qian's mission of the 130s BCE marks its conventional beginning: for the first time a Chinese court opened a lasting door to the west, and that door remained open for some 1,500 years.