A long-rumored network of secret tunnels associated with the Renaissance legend Leonardo da Vinci has been uncovered in Italy.

Italian researchers from Polytechnic University of Milan recently discovered the secret passageways beneath Sforza Castle—using radar, laser scanners, and other groundbreaking technology to verify their hunches.

Construction of the castle in Milan began in 1358, but the landmark was damaged during political unrest and was not finished until a renovation was completed about a hundred years later. Da Vinci was one of several artists eventually hired by the Duke of Milan to decorate the castle’s walls.

During that time period, Da Vinci also created sketches of secret passages underneath a castle. The drawings became famous, generating centuries of speculation. (See images of sketches, which are copyrighted, in a video below…)

Are there secrets buried beneath the castle? Do those passages actually exist?

Now, more than 500 years later, researchers have seemingly verified their accuracy.

“The results were far more significant and intriguing than we had anticipated,” wrote Polytechnic University architectural historian Francesca Biolo, in a recent article on Live Science. “We uncovered rooms on a second underground level and an additional passage running parallel to the known one.”

Da Vinci’s sketches, which date back to the 1490s, featured defensive fortifications below a structure that strongly resembled the silhouette of Sforza Castle.

The building has an extensive network of known underground passageways. One of the tunnels allowed Duke Ludovico to visit the Basilica of Santa Maria delle Grazie, where his late wife who died during childbirth was buried. (That church also contains Da Vinci’s mural of The Last Supper). Some of the Sforza Castle passageways are still accessible today.

However, Biolo and her team of researchers believed the castle was still holding numerous secrets and thought that further exploration would reveal additional discoveries.

They were right.

Just one or two feet below ground

The researchers collaborated with Sforza Castle authorities and the engineering company Codevintec Italiana to conduct their surveys. Hoping to locate passageways or castle spaces that were either inaccessible or not previously identified, they used laser scanning, GPS, 3D ground-penetrating radar, and photogrammetry, which uses numerous photographs to construct a virtual 3D model.

Their efforts discovered a new passageway and additional subterranean rooms – some of which were just 1-2 feet below ground. Soldiers could have used this hidden tunnel to defend the castle in the event of an attack. The study also identified areas for further exploration in the future.

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But perhaps the greatest byproduct of the Polytechnic University exploration is that it provides a little more clarity on a mystery that has prevailed for centuries.

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

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