"Cerca, trova" -- seek and you shall find -- says a tantalizing five-century-old message painted on a fresco in the council hall of Florence's Palazzo Vecchio.
Researchers now believe these cryptic words could be a clue to the location of a long-lost Leonardo da Vinci painting, and they are pressing local authorities to allow them to search for the masterpiece of Renaissance art.
Maurizio Seracini, an Italian art researcher, first noticed the message during a survey of the hall 30 years ago, but his team lacked the technology then to see what lay behind Giorgio Vasari's 16th-century fresco "Battle of Marciano in the Chiana Valley."
However, radar and X-ray scans conducted between 2002 and 2003 have detected a cavity behind the section of wall the message was painted on, and Seracini believes it may conceal Leonardo's unfinished mural painting, the "Battle of Anghiari."
Considered one of Leonardo's greatest works, the mural is known today through the Tuscan master's preparatory studies and copies made by other artists.
"At the time, this was considered the masterpiece of masterpieces," Seracini told the Associated Press. Recovering it "would be like discovering a new Mona Lisa or a new Last Supper."
Leonardo's mural was thought to have been destroyed in the mid-16th century when artist, writer and architect Vasari renovated the hall that once served as Florence's seat of power. He then covered the walls with his own paintings.
Leonardo began working on the "Battle of Anghiari" in June 1505, when he was 53. He worked alongside fellow artist and rival Michelangelo, who had been commissioned to decorate the opposite wall with scenes of the Florentine republic's military triumphs.
Michelangelo never went beyond the preparatory work for his "Battle of Cascina," but Leonardo did paint his battle's centerpiece -- a violent clash of horses and men called the "Fight for the Flag."
Leonardo later abandoned the work and left for Milan. Some chroniclers of the time said the artist had experimented with unstable paints that had rapidly degraded, leaving the painting irreparably damaged.
"For generations these stories have held us back, but there are documents that say otherwise," Seracini said. "Maybe other parts were damaged, but we know that 60 years later, when Vasari began his works, the painting was still visible and people still came to marvel at it."
Vasari raised the hall's roof 23 feet by building a second set of walls, but scans show that at one point he left a space between the two walls that is just large enough to house Leonardo's 19-by-13-foot "Fight for the Flag," Seracini said.
Vasari used a similar technique to preserve other works of art, he said.
"We see from Vasari's writings that Leonardo was just too important to him," Seracini said, adding that Vasari himself may have painted the message on a tiny green flag in his 39-by-26-foot fresco as a clue to the location of "Battle of Anghiari."
"It is the only writing on dozens of flags in that painting," Seracini said. "And what are we looking for if not for something which was already known then as the 'Fight for the Flag'? Can all this be a coincidence?"
Seracini, whose research on another Leonardo painting is quoted in Dan Brown's novel "The Da Vinci Code," is an engineer who has spent the last three decades conducting scientific investigations on art treasures. He said he would like to continue his search for "Battle of Anghiari" but authorities in Florence have denied him a permit.
"For months now we have been at a standstill and since all this is paid for by a private company, at no cost to the municipality, it's difficult for me to understand the reason for this behavior," he said.
Chiara Silla, director of the Palazzo Vecchio museum, said the inquiry hasn't been given the go-ahead because Seracini has yet to present a detailed report on his survey. If authorized to resume, Seracini said he would conduct another series of scans and insert a small probe through Vasari's painting to detect any traces of the pigments Leonardo used. That would require at least another year of work, he said.
If "Battle of Anghiari" is located, it should be possible for conservation artists to remove a section of Vasari's fresco, extract Leonardo's painting and then safely replace the Vasari, Seracini said. He said it would be a fairly routine operation for experts.
Alessandro Vezzosi, a Leonardo expert and director of a museum dedicated to the artist in his home town of Vinci, said he is aware of Seracini's work and that it is based on solid evidence.
"We need to get to the bottom of this. The idea of a Leonardo hidden there is incredibly fascinating," he said.