Page "Balrog" Paragraph 3

Upon the waking of the Elves, the Valar captured Melkor and destroyed his fortresses Utumno and Angband.

But they overlooked the deepest pits, where, with many of Melkor's other allies, the Balrogs fled into hiding.

When Melkor returned to Middle-earth from Valinor, now bearing the epithet Morgoth, he was attacked by Ungoliant, a spider-like creature ; and his piercing scream drew the Balrogs out of hiding to his rescue.