Throughout this week, Neil MacGregor has been exploring the world of the late 7th century, with objects from South America, Britain, Syria and Korea. Today's object is from the 4000 mile tangle of routes that has become known as the Silk Road - that great conduit of ideas, technologies, goods and beliefs that effectively linked the Pacific with the Mediterranean. His chosen object which lets him travel the ancient Silk Route is a fragile painting telling a story of "industrial espionage". It comes from the Buddhist kingdom of Khotan, now in Western China, and tells a powerful story about how the secrets of silk manufacture were passed along the fabled route. The cellist and composer Yo Yo Ma, who has long been fascinated by the Silk Road and who thinks of it as "the internet of antiquity", and the writer Colin Thubron consider the impact of the Silk Road - in reality and on the imagination.Producer: Anthony Denselow