Lord Of The Rings: 10 Best Scenes NOT From The Books
3. The Elves In Helm's Deep - The Two Towers
When Gandalf learns Rohan is set to be attacked by the Uruk-Hai, he encourages the Rohirrim to seek refuge in a fortress called Helm's Deep.
Anticipating this plan, Saruman sends his army to the fortress to wipe the people of Rohan from the face of Middle-Earth. Although the Rohirrim are drastically outnumbered, hundreds of Elves shows up at Helm's Deep in the eleventh hour to assist them against the enemy.
But in the source material, the Elves are entirely absent from the this battle. Peter Jackson explains in the commentary track for LOTR: The Two Towers how Saruman's forces are attacking, not just the lands of Men, but Elves and Ents as well. To illustrate Saruman was a threat to all life on the planet, he wanted to show other races fighting against the White Wizard's army.
Although the Elves fought the Uruk-Hai in their native land in the book, Jackson thought it would be cleaner to show the Elves and Men battling the Uruk-Hai in the same location.
Including the Elves also makes this battle more emotional since it's the first time we see the noble race put their millennia-long rivalry with Men aside for the greater good.