economy and India another 16 percent, according to the calculations of Angus Maddison, a leading British economic historian. Asia's retreat into relative isolation after the expeditions of Zheng He amounted to a catastrophic missed opportunity, one that laid the groundwork for the rise of Europe and, eventually, America. Westerners often attribute their economic advantage today to the intelligence, democratic habits or hard work of their forebears, but a more important reason may well have been the folly of 15th-century Chinese rulers. That is why I came to be fascinated with Zheng He and set out earlier this year to retrace his journeys. I wanted to see what legacy, if any, remained of his achievement, and to figure out why his travels did not remake the world in theway that Columbus's did. heng He lived in Nanjing, the old capital, where I arrived one day in February. Nanjing is a grimy metropolis on the Yangtze River in the heart of China. It has been five centuries since Zheng He's death, and his marks on the city have grown faint. The shipyards that built his fleet are still busy, and the courtyard of what had been his splendid 72-room mansion is now the Zheng He Memorial Park, where children roller-skate and old couples totter around for exercise. But though the park has a small Zheng He museum, it was closed -- for renovation, a caretaker told me, though he knew of no plans to reopen it. I'd heard that Zheng He's tomb is on a hillside outside