This is not a simple question. I once thought it was because the Marine Sillk Road got great development in Song Dyansty, but it is too simple when I read some materials. Silk Road was declining gradually. It initiated in Han Dynasty and created a boom. In the end of 4th Century, mainland China, Rome and Persia in the west end of the link were all in disruption. After a few centuries' dreariness, the booming Tang Dynasty made the road active again, but its power withdraw from Xinjiang in later years. In Yuan Dynsty, Mongolian rulers dredged the Silk Road through its close Khan states. Till Song, Marine Silk Road got uprising for the development of sea transportation. Silk Road was stopped finally along with the death of Qing Dynasty.