Castle walls are thick, sturdy structures built to protect a castle from attacks. Made of stone or brick, these walls were often several feet high and included features like towers and battlements. The height and strength of the walls made it difficult for enemies to breach the castle during sieges. In addition to defense, castle walls often had narrow openings called arrow slits or murder holes for archers to shoot at attackers while remaining safe inside. Some castles also had a moat, a deep ditch filled with water, surrounding the walls to further deter invaders.