§ Of the Fifth Battle: Nirnaeth Arnoediad The Silmarillion

Yet neither by wolf, nor by Balrog, nor by Dragon, would Morgoth have achieved his end, but for the treachery of Men. In this hour the plots of Ulfang were revealed. Many of the Easterlings turned and fled, their hearts being filled with lies and fear; but the sons of Ulfang went over suddenly to Morgoth and drove in upon the rear of the sons of Fëanor, and in the confusion that they wrought they came near to the standard of Maedhros. They reaped not the reward that Morgoth promised them, for Maglor slew Uldor the accursed, the leader in treason, and the sons of Bór slew Ulfast and Ulwarth ere they themselves were slain. But new strength of evil Men came up that Uldor had summoned and kept hidden in the eastern hills, and the host of Maedhros was assailed now on three sides, and it broke, and was scattered, and fled this way and that. Yet fate saved the sons of Fëanor, and though all were wounded none were slain, for they drew together, and gathering a remnant of the Noldor and the Naugrim about them they hewed a way out of the battle and escaped far away towards Mount Dolmed in the east.