The Two Towers Book 3, Chapter 7
They ride into the night before they stop. Gandalf asks Legolas how far it is to Isengard and finds out that it is still many miles away. They ride through the second day and again into the sunset. A horseman approaches King Theoden and tells him that the men of the region are making a stand at an ancient fortress called Helm's Deep. Gandalf advises Theoden to lead his men there while he goes to do an errand. They descend into a deep gorge. His countrymen tell him that an attacking force from Saruman is very great. Eomer says, "'Then let us be swift... Let us drive through such foes as are already between us and the fortress'" Book 3, Chapter 7, pg. 170. They ride into the darkness and encounter small bands of orcs here and there. When they make it to the dike before the fortress, there is a large force at their heels. They pass into the walls to find a strong force already waiting to defend the fortifications. The leader of the region, Erkenbrand, is not to be found and they worry about his safety. Eomer readies the fighting men for battle and the women and children retreat to safer caverns.
Time passes, until another band of Rohan comes riding ahead of an army of orcs. A blinding flash of lightning streaks across the sky and rains pounds the earth. The orcs raise their hideous cry of war and the horde surges before the gates. Eomer and Aragorn fight back the rams at the gates, but the doors are twisted on their hinges. Gimli saves Eomer's life and before long, Legolas has killed twenty orcs with his bow. The sky clears to a low moon and the light bathes on thousands of orcs. Even with Eomer and Aragorn rallying again and again, the men of Rohan grow tired. Some orcs break through the wall, but with Gimli's help, the hole is filled and the orcs slain. They eagerly anticipate dawn even though they know that it will not bear a respite from the battle. A great trumpet blast brings the orcs within the walls and the forces of Rohan retreat to the inner strongholds. As they retreat, Aragorn cannot find Eomer. The orcs use a blasting fire, a creation of Saruman, to sear the walls. Theoden worries about the outcome of the battle: "'It is said that Hornburg has never fallen to assault...but now my heart is doubtful.'" Book 3, Chapter 7, pg. 183.
When dawn comes, Theoden prepares to ride into battle and reinvigorate his weary men. Aragorn looks over the gates in the pale light as the orcs yell for the King to surrender. They laugh and destroy more of the walls. They prepare to rush into the buildings, when horses stream from the walls. Theoden rides out and rallies his men. No group of the enemy can withstand his charge. On the ridge, another rider appears. Shadowfax proudly bears Gandalf. Erkenbrand comes with an army behind him. They rush into the valley and assail the orcs. To watching men, it seems that the trees themselves have entered the gorge and are slaughtering orcs, but it is difficult to see in the early light.