In The Lord of the Rings: The Two Towers, 10,000 Uruk-hai attack Helm’s Deep. Saruman sends the army against the fortress during the Battle of the Hornburg.
The number establishes the overwhelming scale of the assault. The defenders include soldiers of Rohan, civilians sheltering at the Hornburg, and a small group of Elves led by Haldir. The battle therefore presents a much larger attacking force against a heavily outnumbered defense.
The figure is sometimes confused with the size of other armies in the trilogy. The 10,000 attackers are specifically the Uruk-hai force at Helm’s Deep, not the armies at Minas Tirith or the total forces serving Sauron and Saruman.
The film’s battle differs in some details from Tolkien’s novel, including the prominence of the Elven reinforcements and the staging of the assault. The movie nevertheless preserves the central situation: Rohan’s defenders hold a fortified refuge against Saruman’s massed Uruk-hai until Gandalf arrives with Éomer and additional riders.