A merlon is the solid, upright section of a fortified wall's crenellated battlement, alternating with open spaces called crenels. Historically, these architectural features served as vital defensive shields for medieval archers and defenders guarding castle ramparts.

Key Features of a Merlon:
Shielding function: Blocks enemy projectiles, providing full-body cover for defenders during sieges.

Crenel pairing: Alternates systematically with open gaps to allow defenders to shoot and duck back.

Arrow slits: Often features narrow vertical loops (loopholes) in the center to shoot through safely.

Copings: Finished with sloped or capped stone tops to shed rainwater and prevent erosion.

Decorative variants: Evolved in late-medieval Europe into swallow-tail (Ghibelline) or rectangular (Guelph) shapes.

Hoarding support: Sometimes included timber holes to mount overhanging wooden galleries for dropping rocks.