North and South Forks of the Silk Road

The Silk Road is a series of trade routes through regions of the Asian continent mainly connecting Chang'an in China, with Asia Minor and the Mediterranean. Trade on the Silk road was a major factor in the developing of the great civilizations that was connected by the route. The road divides into north and south routes to avoid the Tibetan Plateau. The Tibetan Plateau is not just the largest but also the highest area in the world. It formed due to a full-speed collision of two continental plates. Tibetan Plateau contains Mount Everest and 13 other peaks that reach higher than 8000 meters and hundreds of peaks of 7000 meters of higher. The Plateau averages more than 5000 meters in elevation and with higher elevation the less dense the air is and the harder it is to breath. Due to the physical toll the Tibetan Plateau had on people not accustomed to the area, the trade route was divided and the people either went north or south of the plateau.

Information taken from:
http://www.crystalinks.com/silkroad.html
http://geology.about.com/od/structureslandforms/a/tibetanplat.htm