In 1270 a scholarly Jewish merchant called Jacob d'Ancona set out on a voyage from Italy. A year later, he arrived in China at the coastal metropolis of Zaitun, the "City of Light" (now known as Quanzhou), four years before Marco Polo arrived at Xanadu in 1275. Nothing was known of this epochal journey until 1990, when David Selbourne was shown d'Ancona's account of his travels, a remarkable manuscript that had been hidden from public view for more...