Mysterious secret tunnels sketched by Leonardo da Vinci 530yrs ago may have finally been uncovered under medieval castle

A GROUNDBREAKING discovery has unearthed mysterious tunnels which may have been sketched by Leonardo da Vinci over 500 years ago.

The Italian genius was not only a groundbreaking mathematician but also an expert in military architecture. It is believed that he could have been the mastermind behind the hidden tunnels discovered beneath the Sforza Castle in Milan.

Study for St. James the Greater and a corner pavilion for a castle.
Leonardo da Vinci may be behind secret tunnels underneath a medieval Italian castleCredit: Alamy
Aerial view of Castello Sforzesco in Milan, Italy.
Sfrorza Castle, in Milan, was completed in the 15th centuryCredit: Alamy
Illustration of a map of Milan showing the location of Sforza Castle and newly discovered tunnels, along with images of a da Vinci sketch and an aerial view of the castle.

In sketches dating back to around 1495, the famous inventor made references to subterranean passages beneath the medieval stronghold. These passages were likely designed for soldiers to navigate in case the castle’s defenses were compromised.

This remarkable finding was unveiled by the Polytechnic University of Milan in January. The university conducted a series of surveys aimed at digitally documenting the underground structures of the 15th-century Sforza Castle without causing any damage.

These noninvasive methods include ground-penetrating radar, GPS and laser scanning which can unearth structures without excavation within the castle.

The revealing surveys took place between 2021 and 2023 as a doctoral thesis for Francesca Biolo who is now an architect and research fellow.

She said in an email: “Our findings serve as yet another reminder of how deeply embedded history is within our cities.

“Only through awareness of this fact, combined with a thorough understanding of history and architecture, can we truly appreciate the importance of preserving and enhancing our cultural and architectural heritage.”

Originally her survey was intended to digitise only the area underneath a protective outer wall of the castle called the Ghirlanda – which features well-known passageways accessible to tourists.

But much to the surprise of the scientists, a second secret tunnel which experts had only hypothesised about for a few years was discovered.

This second tunnel runs parallel to the first one, about one metre (three feet) below the surface. 

It is believed that soldiers would have used this secret route to defend and reclaim the Ghirlanda against enemy invaders, Biolo said.

A worker uses ground-penetrating radar on a brick wall in a tunnel.
Other tunnels under the castle were also discovered under Sforza CastleCredit: Politecnico di Milano
Sforza Castle in Milan, Italy.
The castle was built in the 15th century by Francesco Sforza, Duke of Milan from 1450-1466.Credit: Getty

The researchers also uncovered other tunnels, almost all of which were made of brick with a barrel vault creating a curved ceiling.

One of them leads in the direction of the Basilica of Santa Maria delle Grazie, where the Duke of Milan’s wife is buried. 

Commonly known as Ludovico il Moro, the duke served in his position from 1494 to 1498.

It is hypothesised that the grief-stricken duke had the tunnel built to reach his late wife with easy access, but more research is needed to confirm whether the tunnel connects to the Basilica of Santa Maria delle Grazie.

Researchers also believe that there are more subsurface structures to be uncovered, although it’s still not always possible to map everything underground with non-destructive methods, Biolo explained.

The castle used to span an area about six times the size of what still stands today, with the footprint of the building that is currently visible above ground being around 40,000 square meters (430,560 square feet).

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Construction of the Sforza Castle, which is located in the heart of modern-day Milan, began in the mid 1300s.

The site underwent extensive renovations and demolitions at the end of the 19th century during the Napoleonic wars.

“These new findings, however, reveal that not everything was lost,” Biolo added. 

“The underground holds (traces) of our past — not just from this era, but from many others.”

Da Vinci often spent time at Sforza’s caslte during the late 1400s as a member of the Duke’s court.

Sforza commissioned the innovative artist for a painting featured in the property’s Sala delle Asse. 

During this period, Leonardo produced sketches of defensive structures that closely resemble the layout of the Sforza Castle, including the Ghirlanda and multiple passage systems around it.

Dr. Francesca Fiorani, an expert on Da Vinci at the University of Virginia, said: “It is always important to be able to reconstruct the past as precisely and as firmly as possible.

“In the case of Leonardo, we know that most of his drawings, especially the architectural drawings, were ‘mental’ exercises, ideas for innovative buildings.

“But they were not meant as blueprint for actual construction, just ideas of innovative building: paper architecture that existed only as drawings on paper, one might say.”

Bilio is now taking part in a project that looks at the enhancement and preservation of some municipal buildings in other Italian towns.

“Perhaps what I hope for most in the future is not so much a new and groundbreaking discovery, but rather a growing, widespread, and conscious tendency towards the preservation of our heritage,” Bilio added.

She also highlighted the notion that history is everywhere, even in areas where you least expect it.

Aerial view of Castello Sforzesco and Sempione Park in Milan, Italy.
Sforza Castle is located in the heart of Milan, ItalyCredit: Alamy
Ground-penetrating radar survey near Milan's Sforza Castle.
Non-destructive methods were used to locate the secret tunnelsCredit: Politecnico di Milano
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