Bastion fort

A fortress whose projecting bastions provide overlapping fields of fire along its walls and protect them from direct attack.

Bastion: A projecting part of a fortification, usually placed at a corner, from which defenders can fire along adjacent walls. Its flanking fire covers the curtain walls between neighboring bastions.
Medieval fortification: The defensive architecture and military engineering used in Europe during the Middle Ages. Bastion forts developed in response to weaknesses in medieval walls and towers.
Palmanova: A planned star-shaped fortress city in northeastern Italy, founded by the Republic of Venice in 1593. Its geometric plan makes the bastion system visible at the scale of an entire city.
Motte-and-bailey: A medieval fortification consisting of a raised mound and an enclosed courtyard. Its earth-and-timber defenses predate the artillery-resistant bastion system.
Curtain wall: The section of defensive wall connecting two towers or bastions. Bastions protect this vulnerable stretch by firing along its face.
Gunpowder artillery: Artillery that uses gunpowder to launch projectiles against targets. Its growing power made tall, thin medieval walls easier to breach.
Vauban fortifications: The defensive works designed or improved by French military engineer Sébastien Le Prestre de Vauban. Vauban refined bastion defenses into systematic, layered fortification plans.
Concentric castle: A castle with nested defensive walls arranged around a central stronghold. Its high, concentric walls answer threats unlike the bastion fort's low, angular plan.
Ravelin: A detached, usually triangular fortification placed before a fortress wall or gate. It shields the curtain wall and gate from direct artillery fire.
Italian Wars: A series of conflicts fought in Italy and neighboring regions from 1494 to 1559. French artillery attacks in the wars accelerated experimentation with angular defenses.

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Sébastien Le Prestre de VaubanBroader topic: Vauban adapted this angular fortress form to strengthen defenses against artillery.