In January III 3019, the Company of the Ring travelled through Moria on the Quest of Mount Doom. In Gandalf, the Balrog finally encountered a being of the same order and power as itself. As the two Maiar faced each other on the Bridge of Khazad-dûm, Gandalf broke the Bridge and the Balrog fell into the depths, but Gandalf too was drawn into the abyss.

Both survived the fall, and Gandalf pursued the Balrog for eight days through the deepest caverns beneath Moria. At last they came to the Endless Stair, and climbed the steps that led to the peak of Zirakzigil. There Durin's Bane fought its last battle - for two days and nights, the Balrog battled with Gandalf, but at last it was cast from the peak, and broke the mountain-side as it plunged to its doom.