The Silk Road is named for silk, because silk stood at the centre of the trade along these routes. They joined east and west, and merchants, goods, religions and cultures moved along them.
In 138 BCE Zhang Qian set out on Emperor Wu's mission to the Western Regions, opening east-west communication, and so the Silk Road was opened.
In 60 BCE the Han set up the Protectorate of the Western Regions to keep the trade routes north and south of the Tianshan open, more than seventy years after Zhang Qian's mission.
In the 8th and 9th centuries, under the Tang, Silk Road trade reached its height, and Chang'an became the city where Eurasian merchants, religions and cultures met. The span of this class ends in the Ming.
The Silk Road is the class in the chapter on Commerce on the Eurasian trade routes centred on the silk trade, from the Han to the Ming. In 138 BCE Zhang Qian was sent to the Western Regions and opened communication between east and west; the Han set up the Protectorate of the Western Regions to keep the routes open; and in the Tang Chang'an became a city where Eurasian merchants, religions and cultures met.