When did the Silk Road become popular?

Nick, this trade route came into being "accidentally". In 139BC, Zhang Qian was sent by Emperor Wudi of Western Han Dynasty to persuade a country in the west regions to fight the Huns together. Unfortunately, he was captured by the Huns twice and finally returned in 126BC. Although he didn't accomplish his goal to unite that country to fight the Huns, he learnt much knowledge about the Western Regions.

In 60BC, the Huns surrendered to the Western Han Empire. Emperor Xuandi ordered to establish Western Regions Frontier Command to take charge of the Western Regions.

In 166 AD, ancient Roman Empire sent envoys to Luoyang to pay a formal visit to Emperor Huandi of Eastern Han Dynasty. This marks the beginning of cultural communication between the Europe and ancient China. So I think the road became popular at this time.