Following the repeated rebellions in Castel della Pieve, Perugia decided to build the fortress to control the entire city and to protect the presence of its garrison. The plan, a triangular shape, is reflected in the typical cusped forms of Gothic cathedrals: the fortification has five towers. The military structure, built for high security, has fostered over time the installed mercenary captains, such as Biordo Michelotti and Braccio Fortebraccio da Montone. In 1503 Cesare Borgia, known as Valentino, waiting to cross Chiana to attack the Republic of Siena, settled in the fortress and here, in the presence of Niccolo Machiavelli, ordered to be strangled Vitellozzo Vitelli, the Duke of Gravina Francesco Orsini, Paolo Orsini, and Oliverotto Fermo on the grounds that they had conspired against him together with other leaders of central Italy. Since 1529 the fortress lost its military function and became the seat of the Perpetual Governor.