The soundtrack helps you understand and feel what is going on; it played a big role in the movie because the goal was for you to be emotional or in suspense during certain parts of the movie. One part of the movie that was emotional for me was when pippin had to sing for Denethor II while there was a battle going on. During battle scenes and death scenes, the music needs to be intense/sad so that the viewers can feel what the characters are feeling. They even made up their own elvish language and had an elvish song that made it interesting. The soundtrack is what makes the movie
