In J. R. R. Tolkien's's fictional Middle-earth, the Dagor Aglareb was the third battle of the Wars of Beleriand, known as the Glorious Battle.

After the Dagor-nuin-Giliath the Ñoldor of Beleriand had wasted their chance to destroy Morgoth's forces quickly, and instead had been building their numerous realms and establishing contacts with the Sindar.

As the Ered Engrin spewed forth fire, Morgoth sent forth numerous small bands of Orcs, which passed through the Pass of Sirion and Maglor's Gap. Fighting small battles along the way, they penetrated deep in West and East Beleriand, where they were destroyed by southern forces of the Ñoldor and Elves under Círdan of the Falas.

Doriath was shut and refused to fight, and the Laiquendi of Ossiriand fought no more battles after their leader had been killed in the First Battle of Beleriand.

Meanwhile, the main force of the Orcs spewed forth from Angband to Dorthonion, where the twins Angrod and Aegnor held them off until armies under Fingolfin and Maedhros counter-attacked on the plains of Lothlann and Ard-galen, trapping the Orcs between them. Most Orcs were destroyed, and they retreated to Angband. The Ñoldor pursued, and utterly destroyed their enemies in sight of the gates of Angband.

This was the first complete victory over Morgoth, and after it the Ñoldor maintained a guard on Angband, beginning the period of watchful peace known as the Siege of Angband.