Dagor AgalarebDagor Agalareb (60 Y.S.) - Also known as the Third Battle of Beleriand (Dagor-nuin-Giliath being the second), it was an all-out assault by Morgoth in an attempt to drive out the Noldor from Beleriand.

 

"Now Morgoth, believing the report of his spies that the lords of the Noldor were wandering abroad with little thought of war, made trial of the strength and watchfulness of his enemies.  Once more, with little warning, his might was stirred, and suddenly there were earthquakes in the north, and fire came from fissures in the earth, and the Iron Mountains vomited flame; and Orcs poured forth across the plain of Ard-galen.  Thence they thrust down the Pass of Sirion in the west, and in the east they burst through the land of Maglor, in the gap between the hills of Maedhros and the outliers of the Blue Mountains.  But Fingolfin and Maedhros were not sleeping, and while others sought out the scattered bands of Orcs that strayed in Beleriand and did great evil they came upon the main host from either side as it was assaulting Dorthonion; and they defeated the servants of Morgoth, and pursuing them across Ard-galen destroyed them utterly, to the least and last, within sight of Angband's gates.  That was the third great battle of the Wars of Beleriand, and it was named Dagor Agalareb, the Glorious Battle." ~The Silmarillion, chap. 13 (Of the Return of the Noldor)

 

After the battle, Morgoth and the Elves fought what amounted to a war of attrition for almost four centuries.  The Noldor laid siege to Angband but could not penetrate its walls, while the armies of Morgoth did not dare venture forth and engage them in open battle.  The stalemate was finally broken at Dagor Bragollach in 455 Y.S..