Who were the Sangallos, the two architects who revolutionized military fortifications

When talking about military engineering, especially in reference to that of the past, it is impossible not to mention the fortification works designed by Antonio da Sangallo the Elder and his nephew Antonio da Sangallo the Younger. With their works, the two architects contributed decisively to marking the transition from defensive military engineering of the medieval tradition to modern fortification, between the end of the 15th and the beginning of the 16th century.

The artillery problem

With the emergence of new war technologies, military engineers found themselves facing an unprecedented and potentially devastating threat to fortifications, both those inherited from tradition and those of new conception: theartillery. The structures in use up until then, on the one hand, were able to resist attacks carried out with battering rams, ladders or catapultson the other hand they proved to be completely inadequate in the face of cannons. The iron balls fired by the artillery could in fact demolish towers and curtain walls with just a few shots, making traditional defensive solutions obsolete. From a purely design point of view, the old fortifications had different features weak points: the excessive height of the walls and towers made them easy targets to hit, even from a great distance; similarly, the sharp corners of the quadrangular towers they constituted structurally critical points: the impact of even a single cannon shot could compromise their stability, to the point of causing their collapse.

The invention of the bastion

Antonio da Sangallo the Younger revolutionized military engineering by perfecting the solution of bastionor bulwark, key element of modern fortification. It was a protruding and pointed structure, with a shape similar to a spearhead or arrow, designed to counter the effectiveness of artillery. This geometry did not offer flat surfaces on which cannon shots could impact frontally, but favored their deviation, reducing its kinetic energy and, consequently, the destructive capacity. This innovation was accompanied by a profound revision of the walls of the fortifications: the defensive curtains were lowered, made much thicker and inclined towards the outside, giving rise to the so-called escarpment.

On the sides of the bastion, the walls were equipped with gunnerallowing a defense based on cross shot. In this way, the blind spots typical of old fortifications were effectively eliminated, ensuring continuous and more effective control of the defensive perimeter. The choice of materials also responded to precise functional needs: the fortresses were built mainly in bricks, rather than hard stone, and the walls were filled internally with sandy materials. This solution allowed the energy of cannon shots that impacted the external surfaces to be absorbed and dissipated, increasing the overall resistance of the structure.

The fortifications designed by the Sangallo family

Among the most representative examples stands out Fortezza da Basso in Florence, built based on a design by Antonio da Sangallo the Younger in collaboration with Baccio d’Agnolo. Its pentagonal plan constitutes a clear expression of the new concept of military fortification adhering to the San Gallo canons.

Another emblematic case is that of Fortress of Civita Castellananear Viterbo. Commissioned by Pope Julius II and designed by Antonio da Sangallo the Elder together with Bramanteis considered a transitional structure between the medieval and modern models. In fact, the structure retains a central keep, protected and flanked by external bastions, which introduce the new defensive logic linked to artillery.

Castel Sant’Angelo, in Rome, is also among the most significant examples. Here Antonio da Sangallo the Younger he intervened substantially on the pre-existing structure, starting its modernization through the insertion of a polygonal-shaped bastion system.