At last, in the year when Eärendil was seven years old, Morgoth was ready, and he loosed upon Gondolin his Balrogs, and his Orcs, and his wolves; and with them came dragons of the brood of Glaurung, and they were become now many and terrible. Of the deeds of desperate valour there done, by the chieftains of the noble houses and their warriors, and not least by Tuor, much is told in The Fall of Gondolin: of the battle of Ecthelion of the Fountain with Gothmog Lord of Balrogs in the very square of the King, where each slew the other, and of the defence of the tower of Turgon by the people of his household, until the tower was overthrown; and mighty was its fall and the fall of Turgon in its ruin.
Tuor sought to rescue Idril from the sack of the city, but Maeglin had laid hands on her, and on Eärendil; and Tuor fought with Maeglin on the walls, and cast him far out, and his body as it fell smote the rocky slopes of Amon Gwareth thrice ere it pitched into the flames below. Then Tuor and Idril led such remnants of the people of Gondolin as they could gather in the confusion of the burning down the secret way which Idril had prepared.
There was a dreadful pass, Cirith Thoronath it was named, the Eagles' Cleft, where beneath the shadow of the highest peaks a narrow path wound its way; on the right hand it was walled by a precipice, and on the left a dreadful fall leapt into emptiness. Along that narrow way their march was strung, when they were ambushed by Orcs, for Morgoth had set watchers all about the encircling hills; and a Balrog was with them. Then dreadful was their plight, and hardly would they have been saved by the valour of yellow-haired Glorfindel, chief of the House of the Golden Flower of Gondolin, had not Thorondor come timely to their aid.
Many are the songs that have been sung of the duel of Glorfindel with the Balrog upon a pinnacle of rock in that high place; and both fell to ruin in the abyss. (...) Then Thorondor bore up Glorfindel's body out of the abyss, and they buried him in a mound of stones beside the pass; and a green turf came there, and yellow flowers bloomed upon it amid the barrenness of stone, until the world was changed. The Silmarillion (chapter 23)