Changes in warfare and the advent of firearms hastened the renewal of military architecture in the second half of the 15th century. The high walls of the medieval fortress were replaced by thick low-slung bastions more efficient in deflecting cannon fire and withstanding the impact of a direct hit.

Fortresses became full-scale war machines, whose design involved the participation of technical specialists like Luciano Laurana, Baccio Pontelli, the Sangallos, and Francesco di Giorgio. The latter devoted the most important section of his Treatise to military technology. He applied the new fortification principles to the system of fortresses planned by Federico da Montefeltro in the Marca Urbinate, where he arrived at an admirable balance between efficiency and esthetic quality.