For many centuries the Castle and its Borgo constituted the centre of the city's administrative and judicial power.

It was only during the Kingdom of Illyria created by Napoleon, between 1809 and 1813, that the castle's interior was renovated to house a significant number of troops, supplies, weapons, and ammunition. This military purpose was maintained even after the return of the Habsburgs, and the manor continued to be used as a barracks. At the beginning of the 20th century, the castle became a garrison prison and the seat of the military tribunal. In 1914, a military carrier pigeon station was also established there.

As Ranieri Mario Cossar wrote in 1937, at the end of the conflict, the Castle "had the appearance of a colossus mortally wounded. The central building, struck by four 305 mm shells […] seemed as if it would collapse at any moment." Beginning in 1934, the castle was rebuilt in a form as close as possible to its medieval and sixteenth-century appearance. It was reopened to the public on September 7, 1937, in the presence of HRH Duke Amedeo D'Aosta.