It is a long, and satisfyingly complex, story. But it can be summed up with one question: What happened to “The Battle of Anghiari,” a grimacing crunch of men and horses considered by some experts to be Leonardo’s greatest painting?
Mr. Seracini thinks he knows, and he was recently given permission to restart his search, which involves using the most modern detecting equipment to peer through a 500-year-old wall in the Palazzo Vecchio here. On that wall, in 2002, he found a tantalizing crevice behind a Vasari fresco where the Leonardo may be.
If he succeeds, he could bring to light what one Leonardo scholar calls potentially “one of the great art finds of all time.” Or he could find nothing. Or he could find the painting wrecked by time and its own defects. In any case, after three obsessive decades Mr. Seracini is very much on the hook.
“I have to say, there is enough here to make you scratch your head — scratch it to the point of losing your hair,” Mr. Seracini, a dapper 60 with, so far anyway, a full head of white hair, said as he stood in the room where he believes the painting is hidden. “It’s very intimidating.”
One of the few certainties is that the painting, or at least a part of it depicting a fight for a standard, did exist on the wall of the Palazzo Vecchio, the old home of the Medicis.
“Friday the 6th of June, 1505, at the stroke of the 13th hour,” Leonardo wrote in one of his notebooks, “I started to paint in the palace.”
His younger rival, Michelangelo, had also been commissioned to paint his own battle scene on the opposing wall. Michelangelo left for Rome and never began painting it.
But both men produced preparatory cartoons considered not only among the finest ever created but exemplary of the two strains of Renaissance the men embodied: Michelangelo drew heroic bathing nudes; Leonardo worked the motion and fury of men and horses in action.
Vasari called Leonardo’s cartoon “most excellent and masterful for its marvelous treatment of figures in flight.” But Leonardo started much and finished little. Technical problems — he painted not on wet plaster like traditional fresco, but with oils on a wax-impregnated wall — haunted him.
Only a small portion was completed, though it was Leonardo’s largest painting, perhaps 15 feet by 20 feet, and as extraordinary as the cartoon. Several copies were made, one by Rubens. Even in 1549, a letter writer urged a friend to have a look, calling it a “marvelous thing.”
Beginning in the 1560s, Vasari, who also built what is now the Uffizi museum, began to restructure the room. He enlarged it and covered both walls with his own grand battle fresco. Leonardo’s painting disappeared.
But, of course, it was not forgotten.
In the early 1970s, Mr. Seracini, a former medical student studying bioengineering in California, took an art course at U.C.L.A. from one of the leading Leonardo experts, an Italian professor, Carlo Pedretti. In 1975, Mr. Seracini returned to Florence, his hometown, and by chance linked up anew with Mr. Pedretti, who had begun a search for the lost painting, theorizing that it still lay behind Vasari’s fresco.
It was then, on a scaffolding, that Mr. Seracini, a lowly but enthusiastic assistant, found on a flag in Vasari’s painting what he considered a possible sign from Vasari of what lay behind it: the words “Cerca, trova,” or “Seek and ye shall find.”
“I was puzzled, curious,” he said. “I said: ‘O.K., cool it. Maybe its nothing. Maybe it’s a coincidence.’ ”
Mr. Seracini admits that considering the words a clue is not scientific, and though they are friends, Mr. Pedretti dismisses Mr. Seracini’s interest in the words. They were a motto for one of the companies in the battle, he said, not some mysterious clue.
“We Italians are a little inclined to superstition,” he said.