For a guy who claimed to spend 17 years in China as a confidant of Kublai Khan, Marco Polo left a surprisingly skimpy paper trail. No Asian sources mention the footloose Italian. The only record of his 13th-century odyssey through the Far East is the hot air of his own Travels, which was actually an “as told to” penned by a writer of romances. But a set of 14 parchments, now collected and exhaustively studied for the first time, give us a raft of new stories about Polo’s journeys and something notably missing from his own account: maps. If genuine,...