The Battle of the Hornburg is a fictional battle in J. R. R. Tolkien's epic The Lord of the Rings. The battle pitted the forces of the Wizard Saruman against the Rohirrim under King Théoden, who had taken refuge in the mountain fortress of the Hornburg at Helm's Deep. The engagement is also informally known as Battle of Helm's Deep or simply Helm's Deep after that location. An account of the battle is recorded in the climactic chapter "Helm's Deep" of the volume The Two Towers.
In the book The Lord of the Rings, The Two Towers, the size of the initial garrison at Helm's Deep for Rohan was nearly 1,000, but many more were coming into the fort from across Rohan. The estimated number of total Rohirrim defenders was 2,000 by the time Saruman's army arrived. Merry says that the force that left Isengard numbered 10,000 at least, most marching towards Helm's Deep and others heading off to the Fords of Isen. This number is later qualified by Gandalf: "I have about ten thousand Orcs to manage", so considerably more than 10,000 when the Men of Dunland are added. Though the battle appears severely lopsided, as Uruk-hai were much better in battle than simple orcs, the defenders managed to hold the fort until a force of almost 1,000 men on foot led by Gandalf along with a forest of Huorns arrived at dawn in the rear of the hosts of Isengard and surround the Uruks.
After being released from the influence of his malevolent adviser, Gríma Wormtongue, by the benevolent Wizard Gandalf, Théoden set out to the Fords of Isen, where his marshal Erkenbrand was fighting Saruman's forces. However, Théoden found out that they had been scattered. Gandalf advised him to take refuge in the Hornburg fortress of Helm's Deep, an area named after one of their kings. Gandalf then left on an unexplained errand. Théoden's army went to the area, where local people were commanded by a captain called Gamling the Old. Many of the forces there were very old or young. The women and children of Théoden's capital Edoras were safe in Dunharrow, led by the King's niece Éowyn.