Secret Passageways Recorded in Leonardo da Vinci’s Sketches Discovered Beneath a Medieval Castle in Milan

Beneath Sforza Castle in Milan, researchers have discovered a series of secret tunnels—passageways once sketched by the Renaissance artist and scientist Leonardo da Vinci and traversed by a widower sick with grief.

The tunnels were discovered by experts from the Polytechnic University of Milan, who used ground-penetrating radar and laser scanners to map the 15th-century stronghold’s subterranean structures. The imaging revealed cavities and passageways positioned just a foot or two below the ground.

“The aim is to create a digital twin of the Sforza Castle, a digital model that not only shows the current appearance of the castle, but also allows us to explore the past, by revealing ancient structures that are no longer visible,” says Franco Guzzetti, a geomatics researcher at the Polytechnic University of Milan, in a statement.

Workers began building Sforza in 1358, but the castle was destroyed during a period of political unrest about a century later. Francesco Sforza, the duke of Milan, ordered a new castle to be rebuilt on the ruins in 1450. After he died, his son, Ludovico—also known as il Moro, or “the Moor,” because of his dark complexion and hair—secured the Duchy of Milan and continued renovating the castle.

Ludovico hired several artists—including Leonardo, Donato Bramante and Bernardino Zenale—to decorate the structure’s walls. Leonardo’s frescoes can be seen in the castle’s Sala delle Asse, or “Room of Wooden Boards.” During this time, he also documented secret passages built for military purposes under the castle’s ghirlanda (outer wall).

“This passageway is immortalized in Leonardo’s drawings and has long been the subject of legends and considerable speculation,” per the statement. “But now, thanks to technology, it seems that its existence can be confirmed.”

Historical records suggest Ludovico ordered the construction of an underground passageway to allow him easy access to Milan’s Basilica of Santa Maria delle Grazie, where his wife was buried. Ludovico had married Beatrice d’Este, the daughter of the duke of Ferrara, in 1491. As Encyclopedia Britannica writes, their marriage was “unusually harmonious” but short-lived: Beatrice died in childbirth in 1497. Ludovico’s secret tunnel—which may have stretched over half a mile—would have provided the widower private visitations and served as an escape route in case of a siege.

The researchers scanned the castle’s grounds with ground-penetrating radar, which works by emitting radio waves into the earth and sending back signals to an antenna. Eventually, these scans could be used to create augmented reality experiences or virtual visits for tourists, as Claudio Salsi, historical director of the castle’s museums, tells ANSA.

Francesca Biolo, an architect at the Polytechnic University of Milan, says in the statement that the scans are only the first step in unraveling the secrets of Sforza Castle’s tunnels.

“The [ground-penetrating radar] technology has added to our 3D model by providing data about well-known but inaccessible spaces, revealing unknown pathways and suggesting ideas for further research into these secret passages,” she adds.