The Mona Lisa code: is a Leonardo under the surface?

Experts believe they are close to confirming that a lost Leonardo da Vinci masterpiece is hidden in the cavity of a medieval Italian building.

Leonardo's legendary Battle of Anghiari is thought to lie behind the walls of Florence's Palazzo Vecchio town hall. Another Renaissance artist, Giorgio Vasari, was ordered to paint over it in 1563, but it is believed he constructed a new wall over the fresco instead.

In 2005 art detective Maurizio Seracini found evidence of a slim cavity behind Vasari's fresco, The Battle of Marciano, and for the last three months he has used a gamma camera to probe behind the wall without tampering with the Vasari painting. It appears to have paid off, with the discovery of paint of the type used for the Mona Lisa.