In European military architecture, a drum tower is a large, circular fortification tower integrated directly into a castle's outer curtain wall. Characterized by a squat profile where the diameter is often equal to or greater than its total height, these structures became the dominant design choice for defensive architecture from the late 12th century onward.

Key Structural Features:
Defensive Geometry: The curved surface naturally deflects incoming projectiles from siege engines like trebuchets and catapults.

Elimination of Dead Zones: Unlike square towers, the round design removes blind spots at the corners, allowing archers a continuous field of view to track enemies.

Undermining Resistance: Because they lack sharp angles, drum towers are incredibly difficult for sappers to compromise through traditional tunnel undermining.

Thickened Plinths: The bottom of the tower often flares outward into a sloping stone skirt called a talus or glacis. This strengthens the foundation and causes dropped rocks to bounce sideways into attackers.

Internal Layout and Functionality:
Tactical Placement: Designers regularly built drum towers in pairs to flank a secure gatehouse. They were also placed strategically at corners to provide crossfire down intersecting walls.

Multi-tiered Defense: The roof featured a crenellated parapet walk with battlements for soldiers. Archers used the narrow arrow slits built into the lower floors to safely shoot at the invading force.

Internal Segmentation: The interior consisted of multiple stone-vaulted levels connected by a narrow spiral staircase. The lower chambers stored weapons and food supplies while the upper floors provided living quarters for the garrison.