Battle of the Pelennor Fields (3019 T.A.) - The battle for Minas Tirith at the end of the Third Age.  It was Mordor's attempt to break the power of Gondor.

"And now the fighting waxed furious on the fields of the Pelennor; and the din of arms rose upon high, with the crying of men and the neighing of horses.  Horns were blown and trumpets were braying, and the mûmakil were bellowing as they were goaded to war.  Under the south walls of the City the footmen of Gondor now drove against the legions of Morgul that were still gathered there in strength.  But the horsemen rode eastward to the succor of Éomer: Húrin the Tall, Warden of the Keys, and the Lord of Lossarnach, and Hirluin of the Green Hills, and Prince Imrahil the fair with his knights all about him." ~The Return of the King, Book V, chap. 6 (The Battle of the Pelennor Fields)