Stretching from the ancient Chinese capital of Xian across the expanses of Central Asia to Rome, the Silk Road was, for 1,500 years, a vibrant network of arteries that carried the lifeblood of nations across the world. Along a multitude of routes everything was exchanged: exotic goods, art, knowledge, religion, philosophy, disease and war. From the East came silk, precious stones, tea, jade, paper, porcelain, spices and cotton; from the West, horses,...