The Black Gate Opens is the 10th chapter in the first book of Return of the King

• X - The Black Gate Opens - The Army of the West, with Gandalf, Aragorn, Gimli, Legolas and Pippin (but not Merry) marches to the Black Gate. The Mouth of Sauron comes out to discuss terms, and presents tokens which were owned by Frodo; he then departs and the army of Mordor attacks them.