Forte di Sant'Andrea

Forte di Sant'Andrea stands on its own island at the edge of Le Vignole, guarding Venice's sea gate through the Lido. The city saw that entrance as its most exposed point, and the Veronese architect Michele Sanmicheli designed a fortress to hold it. The Council of Ten approved his plan in January 1535, though work on the foundations began only in 1543, under his supervision. You pick out two parts: a central body on the remains of a fifteenth-century tower, an outer bastion for the gun batteries.

In 1547 the builders fired many guns at once against the new walls, and the structure held without damage. The bastion's rectangular openings sit just above the waterline, so its guns could hit ships close to the surface. Behind them lies a long vaulted casemate under an earthwork, once used to store ammunition. The rear, by contrast, was left unprotected on purpose, so a captor could never turn it into a stronghold. Deterrence did most of the work, overawing ambassadors and foreign visitors rather than holding prisoners. Casanova, held there for a few months in the eighteenth century, later wrote the stay into his memoirs. Its guns faced an enemy just once, in April 1797, when the French ship Le Libérateur d'Italie tried to force the port.

Classical order softens all that martial purpose: a doorway clad in white stone, a Doric cornice, bearded heads on the keystones. Sanmicheli worked to the Vitruvian one-to-seven ratio throughout the design. A plaque recalls the Battle of Lepanto, and a relief of the Lion of Saint Mark adorns the same façade. You reach it by boat, and the water around the walls shows the sub-foundation added later to stop it sinking.