The grey mountain range that marched north to south between the land of Hithlum and the Great Sea. It was broken by the inlet of the Firth of Drengist, a passage through which Fëanor led his followers among the Noldor back into Middle-earth. In the south of Dor-lómin, the Ered Lómin met the range of the Ered Wethrin, and so walled off Hithlum and its lesser lands from Beleriand to the south.
The name Ered Lómin means 'Echoing Mountains', but the origin of the name is uncertain. According to some sources, it refers to the echoes of the great cry of Morgoth as he returned into Middle-earth with Ungoliant before Fëanor's own return. According to others, it was merely in the nature of these mountains to produce great echoes. Whatever the origin of the name, it was clearly shared by the land of Dor-lómin, that lay to the southeast of these mountains.