About 600 meters southeast of the city of Bellinzona, at the highest point of the rocky outcrop on which the fortifications of Bellinzona are located, stands the castle of Sasso Corbaro, which was also called castle of Unterwalden from 1506 and the castle of Santa Barbara from 1818. It has the appearance of a typical Sforza fortress, with a wall structure reduced to the simplicity of a geometric figure. Its design is simple: with a square layout, it encloses a small courtyard, the buildings, two corner towers – the keep and the lookout tower – and the crenelated walkway. Unlike the other fortified works in Bellinzona – joined together to form a single integrated system in the late medieval period – the castle is a detached, single complex, isolated on all sides.
The castle of Sasso Corbaro is also the only one of the three castles in Bellinzona for which the exact date that construction work began is known. Although the presence of a tower to control and watch over the territory is documented since the end of the fourteenth century, it was only in the first months of 1479 that construction began of the castle that can still be seen today. That castle was built at great speed to face the increasingly bold incursions of the Confederate armies into the Bellinzona district. It was constructed by order of the Duke by the renowned Florentine architect Benedetto Ferrini, who died of plague in the autumn of the same year. The work was ultimately completed by the ducal engineer Gabriele Ghiringhelli.
In addition to its main defensive function, the castle of Sasso Corbaro was also used as a place to hold prisoners, as evidenced by a documented escape in 1494.