Always cast in a supporting role in the many books about Marco Polo, the great Kubla Khan now takes center stage in a splendid picture-book biography. He is a wonderful subject-a man who liked to live large, building the imperial city of Beijing from scratch, siring a hundred children, throwing birthday bashes for 40,000 guests. He ruled over the greatest empire of the time, one that was lightyears ahead of Western civilization in terms of the arts,...