why was silk road developed?

关于丝绸之路的形成：
The Silk Road:
The Silk Road dates back to the 2nd century B.C.when Zhang Qian went on a business trip to the western countries following this trade thoroughfare linking Asia and Europe.Originating from Chang’an ,the route traveled through Shaanxi Province,the Hexi Corridor in Gansu Province,Xinjiang,Afghanistan,Iran,Iraq and Syria,ending at the eastern shores of the Mediterranean.More than 4000 of its 7000 kilometers were in China.Because China’s silk reached the West along this road,European scholars came to call it the “ Silk Road”.