Francesco di Giorgio
The fortified complex, built in 1481, was designed for Duke Federico III da Montefeltro by Francesco di Giorgio Martini. The latter in his Treatise, places Cagli as first among his six outstanding fortresses, and describes it in great detail with a certain degree of pride. Particularly unusual is the secret passage (the "soccorso coverto") that links the tower to the imposing ruins of the diamond-shaped fortress (demolished in 1502). The fortifications date back to a time when architects like Francesco di Giorgio Martini were testing out innovative solutions to the problems posed by new developments in artillery.