A crownwork is an advanced outwork in early modern bastion fortification systems consisting of a central full bastion and two flanking half-bastions connected by a rear curtain wall. It projects outward from the main fortress to extend control over key terrain, guard bridges, or block high ground.

Key Structural Features:
Central Bastion: A full projecting pentagonal earth-and-masonry work at the head of the crownwork that commands the outer field of fire.

Demi-Bastions: Two half-bastions terminating the outer walls on either side, providing crossfire and protecting the flanks.

Flank Walls: Long connecting walls running back from the outer demi-bastions toward the main fortress layout.

Moat and Glacis: A deep exterior ditch fronted by a low, sloping earthen bank that exposes attackers to direct defenders' fire.

Strategic Purpose:
Terrain Dominance: Erected in the direction of an expected enemy attack or high ground to prevent the enemy from gaining an advantageous artillery setup.

Enfilade Fire: Designed with lower profiles than the main fortress bastions so heavy guns behind it can fire over the outwork safely.

Communication Access: Linked via covered paths and sally ports allowing troops to launch surprise counterattacks.