Iron Mountains

The Iron Mountains (Ered Engrin) was a massive chain of mountains stretching from sea to sea across the northern part of the world. They were created by Morgoth in the time of the Two Lamps, and lasted until the sinking of Beleriand, when they mostly broke off into the sea - though some remnants of the Iron Mountains can still be seen in Forodwaith in the far north of Middle-earth.