The Iron Mountains or Ered Engrin were an immense mountain range in the north, stretching across Middle-earth from east to west. In the west it bent north a hundred leagues from reaching Helcaraxë.
Of old the Iron Mountains came close to touching the Blue Mountains (Ered Luin) in the West to the Red Mountains (Orocarni) of the East, but in the wars between the Valar and Melkor the mountain range was distorted.
After the War of Wrath the Iron Mountains were broken and disappeared, at least the part of their length that lay directly north of Beleriand.
Portrayal in adaptations
Karen Wynn Fonstad, in her book The Atlas of Middle-earth, imagined that remnants of the Iron Mountains after the First Age could perhaps be all the northern mountain ranges of Eriador and Rhovanion: the Mountains of Angmar, the Ered Mithrin, and the Iron Hills, still occupied by Orcs and Dragons until the Third Age. However, this depiction predates publication of The Peoples of Middle-earth, where it is revealed that the Grey Mountains and Iron Hills existed in the First Age independently of the Iron Mountains. It was during this age that the Dwarves of Khazad-dûm first colonized the Iron Hills. They also considered the Grey Mountains, which lay between Khazad-dûm and the Iron Hills, to be part of their territory.
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings, "Part Two: Valinor and Middle-earth before The Lord of the Rings, VI. Quenta Silmarillion", p. 259
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Shaping of Middle-earth, "V. The Ambarkanta: Map IV"
- Karen Wynn Fonstad, The Atlas of Middle-earth p. 78
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Peoples of Middle-earth, "X. Of Dwarves and Men", "Relations of the Longbeard Dwarves and Men", pp. 302-303