A battlement is the distinctive notched top of a castle wall, designed to protect defenders during battle. If you've ever seen a castle in a picture or movie, you've probably noticed those repeating up-and-down sections along the top of the walls. Those sections are battlements, serving both defensive and tactical purposes.

The raised parts are called merlons, and they shield soldiers from arrows and other weapons. The open gaps between them are called crenels or embrasures, and archers would stand behind the merlons and shoot through these openings at attackers below. A defender could pop up to fire an arrow or look out, then duck back down behind the solid protection of the merlon.

Battlements appeared on castles, fortresses, and city walls throughout medieval Europe and beyond. Medieval soldiers would patrol along the walkway behind the battlements, watching for enemies and defending their position from higher ground.

Today, you might see battlements on old castles that have become museums, or even on modern buildings designed to look medieval. The distinctive silhouette of battlements has become so associated with castles that many people instantly recognize it, even if they've never seen a real medieval fortress.