The Silk Road was an ancient trade route linking China and imperial Rome. It was about 6000 km long, stretching by various routes from the Chinese capital Chang'an, through central Asia to the Mediterranean ports of Alexandria and Antioch, with connected roads leading to India and southeastern Asia. The Silk Road began to be used around 100 B.C.E., after Emperor Wu Ti of China's Han dynasty subdued large areas of Central Asia by conquest and alliance. The area's new stability, and extensive Han road building, enabled caravan traffic to travel these vast distances, which favored high-value goods: silk from China; wool and silver from Rome; and gold in both directions. Ideas also traveled to and from China along the Silk Road: Nestorianism, a sect of Christianity, was introduced into China from Europe and Buddhism came to China from India.
The Silk Road fell into disuse when the Roman Empire disintegrated in the 5th century C.E., and safety conditions deteriorated after nomadic tribes and bands of thieves came to control sections of the route. It was used intermittently thereafter during subsequent, more orderly periods, especially under the Mongol Yuan dynasty begun by Genghiz Khan.