A part of the long northern range known as Ered Wethrin, the Mountains of Shadow, that marked the southern and eastern borders of Hithlum, Mithrim and Dor-lómin to the north of Beleriand. The term is not explained in detail, but presumably applied to the stretch of this mountain chain that ran for some seventy miles along the southeastward fringe of Dor-lómin, including the peak of Amon Darthir. In the southern foothills of these mountains were the Pools of Ivrin, where Narog rose, and the river Teiglin also had its springs beneath the peaks of the Mountains of Dor-lómin.