A recent study led by the Politecnico di Milano uncovered a series of underground tunnels beneath Sforza Castle, some of which could have matched the secret routes drawn by Leonardo da Vinci. This research, part of a PhD project and conducted in collaboration with the castle authorities and Codevintec Italiana, used cutting-edge technology to uncover long-lost military and possibly personal tunnels hidden beneath the historic fortress.
The study used advanced ground-penetrating radar (GPR) and laser scanners to generate a detailed map of the castle’s subterranean structures. The scans revealed cavities and passageways just a few feet below the surface, confirming the existence of long-speculated underground routes. One of the most intriguing discoveries was a tunnel believed to have been commissioned by Ludovico Sforza, also known as Ludovico il Moro, to connect the castle with the Basilica of Santa Maria delle Grazie, where his wife, Beatrice d’Este, was laid to rest.
Historical accounts suggest that Ludovico, grief-stricken after Beatrice’s untimely death in 1497, used this secret passage for private visits to her tomb. The tunnel may have also served as an escape route in times of siege.
Franco Guzzetti, a professor of geomatics at the Politecnico di Milano, explained: “The goal is to create a digital twin of the Sforza Castle, a digital model that not only represents the current appearance of the Castle but also allows you to explore the past, recovering historical elements that are no longer visible.” Enhanced with GPR and 3D laser scan data, this digital reconstruction will allow historians and the public to visualize these hidden spaces and gain insight into how the castle developed architecturally.
Leonardo da Vinci, who worked under Ludovico il Moro, was deeply involved in military engineering and fortification designs. His surviving sketches include depictions of defensive structures strikingly similar to the underground passageways uncovered in this study. However, as Francesca Biolo, an architect at the Politecnico di Milano, cautioned, while Leonardo’s knowledge of military structures was extensive, “it is not possible to determine the exact extent of his involvement in the construction of these tunnels.
The research team, including Biolo, worked with the Sforza Castle authorities to help digitize the fortress’s complex and multilayered architecture. They employed laser scanning, GPS mapping, 3D GPR surveys, and photogrammetry, which combines different images into a virtual 3D model. The discoveries exceeded expectations. “We uncovered rooms on a second underground level and an additional passage running parallel to the known one,” Biolo said, adding that further structures might still be undiscovered under the castle.
Very little physical excavation can be done in the tunnels, as the integrity of the castle and the restrictions of urban planning make that difficult. Instead, researchers plan to bring augmented reality and virtual tours to the castle, allowing visitors to explore these hidden passageways digitally.
More information: Politecnico di Milano
