INTERNATIONAL TRADE IS like sex, The Economist would say. Each generation thinks that it has discovered it for itself. In fact, the proportion of most countries' GDP that is traded internationally has remained remarkably stable over the past hundred years. But the overall volume has gone up so much that globalisation seems like something new. The Silk Road shows us just how little human nature has changed, how adventurous and profit-minded our forebears were. It comes as a shock - rather as if one found explicit sepia photographs of one's grandparents experimenting in depraved positions.

lt is an enormous and beautiful book. The author has travelled the entire length of the Silk Road over the past ten years with his wife, an accomplished photographer, and they have produced the most informative work on the subject I have yet seen. The Silk Road is a very