Art, history, and modern technology helped researchers unveil hidden tunnels beneath Milan’s Castello Sforzesco (Sforza Castle), structures that perfectly match sketches made by Leonardo da Vinci over five centuries ago.
Built in the 15th century, the Sforza Castle had been originally commissioned by Galeazzo II Visconti in the late 14th century; it was later expanded and fortified by the Sforza dynasty, becoming a symbol of ducal power, of the Sforza family, and of Milan itself. The castle’s sturdy walls and strategic design pay tribute to the military architecture of the time, which dutifully created dwellings at once luxurious and incredibly well-defended.
Within this fortress, Leonardo da Vinci played a crucial role, as he worked not only as an artist but as an engineer and a visionary. His association with the castle began in the late 15th century when Ludovico Sforza, the Duke of Milan, invited him to court. During his tenure, Leonardo worked on a variety of projects, including the magnificent frescoes in the Sala delle Asse, a masterpiece of nature-inspired art. However, beyond the visible artistic achievements, his notebooks reveal a much deeper involvement in the structural and defensive aspects of the castle. Among the pages of the Codex Forster I we find detailed sketches and architectural notes outlining underground passages, which, until recently, had been considered purely hypothetical.
For centuries, historians and scholars speculated about the existence of these tunnels and, while Milanese lore often hinted at secret passageways beneath the castle, no definitive proof had ever been uncovered. That changed with the advent of modern non-invasive archaeological techniques. A collaborative effort between the Polytechnic University of Milan and Codevintec, a company specializing in advanced high-tech instrumentation for Earth and Marine Sciences, employed ground-penetrating radar and laser scanning to explore the castle’s substructures without disrupting the historic site. The research team utilized electromagnetic pulses to detect anomalies underground, identifying spaces that suggested hollow passageways. These findings were then further refined using laser scanning, allowing for the creation of highly detailed 3D models of the underground network. The results confirmed what many had suspected: an extensive system of tunnels lay hidden beneath the fortress, their design remarkably similar to Leonardo’s centuries-old sketches.
The newly uncovered tunnels appear to have served multiple functions: some sections propose a clear military application, likely facilitating the discreet movement of troops and supplies to reinforce the castle’s defenses in times of siege. Other passages hint at more personal and ceremonial uses, with one tunnel in particular showing signs that it may have connected the castle to key sites within Milan, including the Basilica of Santa Maria delle Grazie, home to Leonardo’s famed mural, The Last Supper. This particular passage could have provided Ludovico Sforza with private access to the basilica, particularly significant given his deep personal connection to the church: his wife, Beatrice d’Este, is buried there, and it is believed that he spent considerable time in mourning following her death, possibly seeking solace in the sacred space. If the tunnel indeed provided a secret route, it would not only further underscore the political and military importance of the castle but also its intimate connection to the personal lives of its most famous residents.
Leonardo’s architectural vision is evident in the careful planning and execution of these subterranean structures: his designs emphasize both functionality and aesthetics, by integrating complex defensive mechanisms within the castle’s architecture. The passageways were constructed with precision, ensuring stability and longevity, and their strategic placement within the castle’s foundation demonstrates an advanced understanding of military logistics and urban planning.
The success of this research is a significant breakthrough not only for historians but also for the field of modern archaeology: the use of non-invasive technologies in historical investigations allows scholars to uncover new aspects of the past without disturbing fragile structures. This approach has set a precedent for future explorations in densely populated urban areas, where traditional excavation would be nearly impossible. In the case of the Sforza Castle, these findings have sparked renewed interest in the site’s history, raising the possibility of further discoveries beneath the city of Milan itself.
As a next step, researchers are considering the development of a digital twin of the Sforza Castle, which would recreate both its current state and its historical configurations. Thanks to it, scholars and the public alike could explore its structure, architecture, and history in more detail. Such an initiative could allow visitors to virtually walk through the newly uncovered tunnels, providing unprecedented access to an interesting piece of history. Perhaps even more importantly, virtual access to the tunnels could help researchers further their understanding of their use, as well as potentially offer insights into the existence of other similar structures around the city. Additionally, the digital twin would serve as an invaluable resource for preservation efforts, as it would support the studying and monitoring of the castle’s structural integrity in a depth never achieved before.
To us bystanders — perhaps not entirely apt and equipped to understand the architectural and historical ramifications of the discovery — the tunnels speak especially of Leonardo’s ingenuity and of his many incredible talents, reinforcing his legacy as a thinker far ahead of his era. At the same time, we are also reminded of the seemingly inexhaustible depth of history and art still awaiting discovery around Italy, where every day, it can be truly said, brings about a new discovery.
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