The main purpose of bastions in forts is to enhance defensive firepower by eliminating blind spots or "dead ground" around the fort walls, allowing defenders to fire upon any attackers approaching the fort from multiple directions. Bastions project outward from the curtain walls, typically positioned at the corners, and are designed with two faces and two flanks. This angular shape enables defenders to cover the curtain walls and adjacent bastions with overlapping fields of fire, preventing attackers from finding sheltered spots near the walls

. Bastions replaced medieval towers, which were higher but more vulnerable to artillery and had curved surfaces that created dead zones. In contrast, bastions are lower, flat-sided, and constructed with thick earthen ramparts backed by masonry retaining walls. This design absorbs cannon fire effectively while providing space for mounting cannons and maneuvering their crews. The ditch and glacis in front of bastions further protect them from direct artillery fire and make scaling difficult for attackers

. Overall, bastions serve as strongpoints in a fort's defensive perimeter, maximizing the effectiveness of gunpowder weapons and creating a star-shaped fort layout that covers all approaches with interlocking fields of fire