§ Of Beleriand and Its Realms The Silmarillion

This dividing fall was named Andram, the Long Wall, from Nargothrond to Ramdal, the Wall's End, in East Beleriand. But in the east it became ever less sheer, for the vale of Gelion sloped steadily southward, and Gelion had neither fall nor rapids throughout his course, but was ever swifter than was Sirion. Between Ramdal and Gelion there stood a single hill of great extent and gentle slopes, but seeming mightier than it was, for it stood alone; and that hill was named Amon Ereb. Upon Amon Ereb died Denethor, lord of the Nandor that dwelt in Ossiriand, who marched to the aid of Thingol against Morgoth in those days when the Orcs first came down in force, and broke the starlit peace of Beleriand; and upon that hill Maedhros dwelt after the great defeat. But south of the Andram, between Sirion and Gelion, was a wild land of tangled forest in which no folk went, save here and there a few Dark Elves wandering; Taur-im-Duinath it was named, the Forest between the Rivers.