The Hornburg was a great Gondorian fortress situated on the Hornrock, connected to the Deeping Wall. Later it came into the possession of Rohan and the master of Westfold dwelt there. It guarded Helm's Deep nestled in the northeastern White Mountains.
During the War of the Ring it was commanded by Gamling the Old, and defended off a large-scale attack from Isengard during the Battle of the Hornburg. It was said among the Rohirrim that "no enemy has yet taken the Hornburg", and it was considered the strongest point in Rohan, stronger than Edoras and Dunharrow.