It's a centuries-old mystery: Who was the woman behind da Vinci's enigmatic Mona Lisa? Italian researchers say they may soon know: They have discovered the burial place of Lisa Gherardini, the wife of a rich silk merchant who is thought to be the model for the famous painting. They plan to identify her by digging up her 500-year-old bones from the Convent of St. Ursula in central Florence, where she was allegedly buried. Some experts say the bones are too old to reveal any conclusive evidence. But project leader Silvio Vinceti has been studying da Vinci's painting for months and claims to have found hidden symbols in the portrait. If successful, he says he believes the research will unearth characteristics of Gherardini's face that either match or don't match the Mona Lisa, and reveal whether or not she was a model for the painting.