The forces of Saruman, common Orcs and Uruk-hai, along with some orc-human hybrids (called "half-orcs and goblin-men" – which may have referred to or included the Uruk-hai themselves) and human Dunlendings, arrived at the valley of Helm's Deep in the middle of the night during a storm. Meanwhile, Legolasthe Elf and Gimli the Dwarf agreed to compete to see which one could kill the most orcs.
The attackers quickly scaled over the first defence, Helm's Dike, forcing the defenders there to fall back to the fortress. When the Orcs were close, the defenders drove them back with arrows and stones, but they managed to get close to the wall after multiple charges. They attempted to break down the gate with a battering ram, but a sortie led by Aragorn and Éomer scattered the forces.
The Orcs and Dunlendings then raised hundreds of ladders to scale the wall. Aragorn and Éomer repeatedly motivated the tired defenders to repel the Orcs coming up the ladders. However, some Orcs had crept in through a culvert which let a stream out of Helm's Deep, and while the defenders were busy with the assault on the wall, they were suddenly attacked from behind. This was repulsed and the culvert was blocked up under Gimli's supervision.
However, the enemies re-entered the culvert and blasted a wide hole in the wall using an ambiguous explosive device invented by Saruman, a "blasting-fire". Some defenders then retreated to the Glittering Caves, Éomer, Gamling and Gimli among them, while others including Aragorn and Legolas retreated to the burg itself.
Soon Saruman's forces broke through the gate and gained entrance to the fortress. At this moment, however, the horn of King Helm was sounded, and a cavalry charge led by Théoden and Aragorn rode forth, followed by all the Rohirrim left inside. They cut their way through the Orcs and drove them back from the fortress walls.