A small town in northern Italy is basking in new-found celebrity after an Italian art historian claimed it featured in the background of the world's most famous painting – Leonardo da Vinci's Mona Lisa.

A bridge and a road glimpsed over the shoulder of the Mona Lisa, often believed to be imaginary, belong to Bobbio in northern Italy, according to Carla Glori, who says that a numerical code recently discovered on the canvas backs her conclusions.

"The twisting road from the painting can be found there, as is the arched bridge that Da Vinci would have seen from the windows of the town's castle," said Glori, who is due to publish her findings about the Renaissance painting this year.

Glori reached her conclusion while investigating the possibility that Bianca Giovanna Sforza, the daughter of Ludovico Sforza, the 15th century duke of Milan, sat for Da Vinci, and not Lisa del Giocondo in Florence, as is widely believed. "Ludovico controlled Bobbio and Da Vinci likely visited the famous library there like many other artists and scientists based at Ludovico's court," she said.

A small medieval town whose abbey was a model for Umberto Eco in The Name of the Rose, Bobbio and its Roman bridge sit astride the Trebbia valley, which was once described by Ernest Hemingway as the most beautiful in the world.

A group of Italian researchers last year claimed that Da Vinci had painted the number 72 in tiny figures under an arch of the bridge, a reference Glori said is to 1472, when the bridge was almost destroyed by flooding before being rebuilt.

But Silvano Vinceti, the head of researchers, said on Sunday he believed the number was instead a veiled reference to the mystical theories Da Vinci picked up on in Florence.

"There is no Dan Brown code here, just messages that reveal his thinking," he said. "Both the numbers seven and two are very important in the Kabbalism."

Vinceti's team are also studying candidates from the court of Ludovico as possible sitters for the Mona Lisa. "But we believe Bianca Giovanna Sforza is unlikely because she died at 15 and the sitter is at least 22," he said. Glori said she believed Da Vinci may have aged Sforza's face over the years he spent finishing the painting in a bid to hide her identity following her father's downfall.

Martin Kemp, a renowned Da Vinci scholar, said that he was not convinced. "The portrait is almost certainly of Lisa del Giocondo, however unromantic and un-mysterious that idea might be," he said, adding that he also had his doubts on Bobbio. "Leonardo is remaking an archetypal landscape on the basis of his knowledge of the 'body of the earth'."