§ Of Tuor and the Fall of Gondolin The Silmarillion

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.