Historian Donald Sassoon tells Jim Fleming that the Mona Lisa is a great painting, but that other factors conspired to make it an international icon. La Giaconda became a symbol of the Renaissance, and during the nineteenth century, the painting caused a furor when it was stolen from the Louvre and recovered two years later. Now Mona Lisa inspires tourists and helps peddle all sorts of products. Sassoon’s book about her is “Becoming Mona Lisa.”