It is a mystery that has confounded the art world for generations: what became of the Leonardo masterpiece, described as miraculous for its breathtaking beauty and scale, which has not been seen for 500 years? First, the facts: in 1505 Leonardo da Vinci began a vast work, The Battle of Anghiari, on a wall in the Palazzo Vecchio in Florence. The work, a whirl of horses and soldiers in battle, was to commemorate Florence's defeat of Milanese forces in 1440. It was described at the time as a miraculous thing. What happened next is less than clear. It is not even known if the painting was finished, or whether it later suffered irreparable damage. The work vanished and, in the process, became a mystery worthy of Dan Brown's fictional thriller, The Da Vinci Code. Now art experts, backed by a British foundation, say that they are convinced that the masterpiece is hidden behind a later Renaissance fresco, and the one real person to feature in The Da Vinci Code wants to pierce a hole in it and use an endoscope to prove that the masterpiece lies behind it. But Maurizio Seracini, an engineer who specialises in using medical techniques to investigate artworks, faces opposition from fellow art historians who claim that the lost Leonardo is a myth and fear that the huge Giorgio Vasari painting that covers an entire wall in the council chamber of the Palazzo Vecchio will suffer extensive damage for no good reason. On Signor Seracini's side are Carlo Pedretti, Italy's foremost Leonardo expert and head of the Armand Hammer Centre for Leonardo Studies in California, and Rab Hatfield, a Florence-based American expert on the Renaissance. Signor Seracini's initial tests have been funded by the Kalpa group, a charitable foundation set up by Loel Guinness of the wealthy Guinness dynasty. Leonardo was commissioned to paint The Battle of Anghiari in the early 16th century, during the short-lived Florentine Republic that overthrew the Medici dukes. However, the Medicis returned to power, and in 1563 Duke Cosimo apparently instructed Vasari to paint The Battle of Marciano, depicting one of the Medicis' own victories, apparently replacing Leonardo's work. Signor Seracini says that he does not believe that Vasari destroyed the Leonardo. "Instead he erected a wall between his painting and Leonardo's," he says. "In fact, I am convinced he used the Leonardo as a model for his own work." Vasari even left behind a clue worthy of Dan Brown, says Signor Seracini. One of the pennants in his battle scene bears the words Cerca Trova, Italian for "seek and you shall find". Signor Seracini has announced that georadar and thermographic soundings have detected a cavity behind the Vasari. He adds: "All I need to do is make a 4mm hole and feed an endoscope through it with a light and micro camera to tell you whether the Leonardo is there or not." The Florence authorities have yet to give permission. But Signor Seracini insists that the proposed technique is less invasive than most restorations. Professor Pedretti says that he also believes the Leonardo is there, "and it is surely right to look for it". He says that archive documents suggested that Vasari who revered Leonardo, describing him in his celebrated Lives of the Artists as a "brilliant genius who leaves other men far behind" had placed a layer of plaster over The Battle of Anghiari to protect it. Signor Seracini, who has degrees in electronic engineering and medicine and studied art history with Professor Pedretti, has faced criticism for lacking qualifications as an art historian. "I have been working on this theory for 30 years," he says. "The basis of art history, after all, is scientific study." He says that it is "not a treasure hunt or a personal mission. What we are looking for is a painting which at the time was considered the greatest masterpiece ever produced." Signor Seracini came to world attention when he discovered that Leonardo's Adoration of the Magi in the Uffizi Gallery in Florence had been heavily painted over by other artists. He began his soundings in Palazzo Vecchio five years ago and says that he needs another year to prove his case. But Alessandro Cecchi, head of medieval and early Renaissance painting at the Uffizi, says that it is "wrong to violate an historic fresco in the search for something that may not even be there".