This old stone fortress is the centerpiece of the movie's climax. Set deep within the mountains, it's protected on three of its sides, while the fourth is barricaded by a great wall. Helm's Deep is a bastion of strength and security. It is a place where the Rohirrim have defended themselves for many generations. It is a haven against the tides of war that might be a symbol of preservation, resilience, and fortitude:

THÉODEN: They will break upon this fortress like water on rock. Saruman's hordes will pillage and burn.

But we have to think of Helm's Deep contextually, and not just as a super-awesome fortress that's protected Rohirrim through the ages. Why does Théoden order his people to flee Edoras and make for the safety of Helm's Deep? Is it purely out of necessity? Does he have no other option?

Théoden might think so, but Gandalf, Aragorn & Co. think otherwise. Gandalf wants Théoden to stand and fight Saruman's armies. He wants him to defend his homeland and taking his fight to the enemy. He warns that "there is no way out of that ravine. Théoden is walking into a trap." But Théoden refuses, trusting in the legacy of Helm's Deep. He brings his people into a place with no escape, where Gandalf worries they will be slaughtered.

In this sense, Helm's Deep is a symbol of passivity: of not taking action when action is required. Fleeing to Helm's Deep shows Théoden's lack of faith in the strength of his people; it's much easier to hide behind stone than face the legions of orcs head on.

But let's think about this a different way. Was Helm's Deep successful in protecting the Rohirrim? Yeah, it actually was. What chances would the Rohirrim have had out in the open, where the odds were not in their favor? They needed to hide behind some history-tested stone walls while Gandalf went out and secured some extra troops.

So maybe Helm's Deep also represents the sensibility of self-preservation against reckless faith. When you're fighting an enemy as strong as Sauron's, you sometimes need to chill out in a mountain fortress and wait while the White Wizard goes and grabs some extra soldiers.