Out of the heart of China into the mountains of Central Asia, across Northern Afghanistan and the plains of Iran into Kurdish Turkey, Colin Thubron undertakes a journey along the greatest land route on earth -- the Silk Road. Travelling 7,000 miles in eight months, he traces the passage not only of trade and armies, but of ideas, religions and inventions. He meets some fascinating people and encounters some of the world's discontented margins, where the true boundaries are not political borders but the frontiers of tribe, ethnicity, language and religion.