"It crosses the roof of the world, winding more than 2,400 tortuous miles across 20 mountain chains and two desert plateaus. It spans four great rivers, and cuts through the territory of 26 different ethnic groups. This is the ancient Tea Road, which opens Southwest China onto Tibet and thereby Nepal, India, Persia, Mongolia and Russia, and then Europe. The legendary Tea Road was crossed by Marco Polo during his travels, but used by innumerable horse...