Beijing — At the north end of Beijing's Imperial Palace stands Coal Hill, a man-made summit built with the sweat and blood of countless labourers. Climb it and you can absorb a sight that for 500 years, only emperors and their retainers could see: the inner precincts of the Forbidden City. With its arching, tiled roofs of mustard yellow and its high vermillion walls, this is the secret heart of the most inward-looking empire the world has ever seen. For centuries, China shut itself off from the rest of humanity. Secure in its cultural superiority, disdainful of Western ideas and...