Bastion (from French bastillon, diminutive of bastille — "fortress") is a structure projecting outward from the curtain wall of a fortification, most commonly angular in shape and positioned at the corners of the fort. The fully developed bastion consists of two faces and two flanks, with fire from the flanks able to protect the curtain wall and adjacent bastions. As a key element of military architecture, the bastion was central to the style of fortification dominant from the mid-16th to mid-19th centuries, often referred to as the trace italienne or star fort.
Etymology
The word entered English from French bastillon, a diminutive of bastille, meaning "fortress" or "fortified tower." It is related to the Italian bastione and the Late Latin bastire ("to build").
Historical Development
By the mid-15th century, artillery had become powerful enough to render traditional medieval round towers and curtain walls obsolete. The fall of Constantinople in 1453 to large Turkish cannons and the campaigns of Charles VII of France during the Hundred Years' War demonstrated the vulnerability of older fortifications. In response, military engineers developed the bastion as a low, angular projection that could withstand cannon fire while providing overlapping fields of defensive fire.
During the Eighty Years' War (1568–1648), Dutch military engineers further refined the concept by lengthening the bastion faces and shortening curtain walls, producing a construction called a bolwerk. V-shaped outworks known as ravelins were placed in front of bastions and curtain walls for additional protection. These ideas were later systematized and perfected by the French military engineer Sébastien Le Prestre de Vauban (1633–1707), whose fortifications remained in use through the Napoleonic Wars.
Design and Characteristics
Bastions differ from medieval towers in several key respects:
- Height: Bastions are lower than towers and normally of similar height to the adjacent curtain wall. The lower profile made them harder for artillery to destroy, unlike tall towers that presented easy targets.
- Shape: Unlike curved medieval towers, bastions (apart from early examples) were flat-sided, eliminating "dead ground" and allowing defenders to fire upon any point directly in front.
- Construction: Surviving examples are typically faced with masonry, but this served only as a retaining wall. Cannonballs were expected to pass through the masonry and be absorbed by a greater thickness of hard-packed earth or rubble behind. The top of the bastion was left unmasoned to avoid lethal stone shards from cannonball impacts.
- Defensive features: A ditch (moat) typically ran in front of the bastion, with a sloping glacis on the opposite side that shielded most of the bastion from direct cannon fire while making scaling difficult.
- Size: Bastions cover a larger area than most towers, allowing more cannons to be mounted and providing sufficient space for crews to operate them.
Types of Bastions
Various kinds of bastions have been used throughout history:
- Solid bastion: Filled entirely with earth, with the ground level even with the height of the rampart.
- Void (hollow) bastion: Has a rampart or parapet only around the flanks and faces, leaving an empty space toward the centre.
- Flat bastion: Built in the middle of a curtain or enclosed court when the court is too large to be defended by corner bastions.
- Cut bastion: Has a re-entering angle at the point (also called a bastion with a tenaille), used when the angle would otherwise be too acute.
- Composed bastion: Built when the two sides of the interior polygon are very unequal, resulting in unequal gorges.
- Regular bastion: Has proportionate faces, flanks, and gorges.
- Deformed (irregular) bastion: Lacks one of its demi-gorges due to a short interior polygon side.
- Demi-bastion: Has only one face and one flank, used before hornworks or crownworks.
Figurative Usage
In modern English, "bastion" is also used figuratively to describe any institution, group, or person that upholds or defends a particular belief, tradition, or way of life, especially one perceived as threatened or in decline. For example, a "bastion of democracy" or a "bastion of tradition."
Notable Examples
- Castillo de San Marcos (completed 1695), St. Augustine, Florida — a four-bastion fortress.
- Petersberg Citadel, Erfurt, Germany — includes Bastion Franz (c. 1675).
- Neuf-Brisach, France — a Vauban-designed star fortress.
- Komárno Fortress, Slovakia — contains preserved bastions.
- Cittadella, Gozo, Malta — includes St. Martin's Demi-Bastion (1614).
- Nahargarh Fort, Jaipur, India — features bastions in the Rajput architectural tradition.
Obsolescence
Bastion fortifications became largely obsolete in the 19th century with the development of more powerful rifled artillery and high-explosive shells, which could destroy masonry-faced earthworks. They were succeeded by polygonal forts and later by concrete-reinforced defensive positions.
