The Silk Road is not a place, but a journey, a route from the edges of the Mediterranean to the central plains of China, through high mountains and inhospitable deserts. For thousands of years its history has been a traveler's history, of brief encounters in desert towns, snowbound passes and nameless forts. It was the conduit that first brought Buddhism, Christianity and Islam into China, and the site of much of the "Great Game" between 19th-century empires. Today, its central section encompasses several former Soviet republics, and the Chinese Autonomous Region of Xinjiang. The ancient...