Helm's Deep

Helm's Deep is a huge fortress in J.R.R Tolkien's Lord of the Rings trilogy. It plays a prominent role in the second book in the trilogy - the Two Towers, where it is the site of a battle between Saruman's Uruk-hai and the Rohirrim of King Théoden, assisted by Aragorn, Legolas and Gimli (as well as a contingent of elves led by Haldir, if you're talking Movieverse. The defenders are greatly outnumbered, and gradually lose more and more ground, before getting rescued by timely reinforcements from Gandalf and Erkenbrand.