Now the people of Caranthir dwelt furthest east beyond the upper waters of Gelion, about Lake Helevorn under Mount Rerir and to the southward; and they climbed the heights of Ered Luin and looked eastward in wonder, for wild and wide it seemed to them were the lands of Middle-earth.
- The Silmarillion, Chapter 13
Once home to a fortress of one of the Sons of Fëanor, Mount Rerir was a great mountain in the First Age. Likely abandoned after the Battle of Sudden Flame, the War of Wrath left the once mighty mountain greatly diminished.