Utumno (Quenya for "Underworld" or "Hell", Udûn in Sindarin) was the first fortress of Melkor in the far north of Middle-earth. Utumno was built by Melkor after his first expulsion from Arda. The Valar had by this time created the Two Lamps, and Utumno was built around Valian Year 3400 under the Iron Mountains, where the light of Illuin was very dim. Melkor established a second fortress at the western end of the Ered Engrin to act as the first line of defense for Utumno. This became Angband, which was at first held by Sauron. After the destruction of Utumno, Melkor chose to rebuild and fortify Angband as his lair.
