Amon Ereb (S. "Lonely Hill"), sometimes just Ereb, was the broad, shallow-sided hill that dominated the southern plains of East Beleriand.
The hill was the highest point in that region and the easternmost hill of Andram, but was standing alone. Within sight of the Gelion, it had tremendous strategic importance, because it guarded the eastern passage around the Long Wall of the Andram into the southern parts of East Beleriand and the northern Taur-im-Duinath.
It was here that Denethor of the Nandor met his end in the First Battle. Much later, Caranthir fortified it to guard his escape into the south after the Dagor Bragollach in F.A. 455 and the Fëanorions withdrew there after Nirnaeth Arnoediad in F.A. 472. But only after that, in F.A. 540, Morgoth captured the hill driving the last remaining Sons of Fëanor, Maedhros and Maglor, to retreat further south to the Isle of Balar.
Fate
A small circle appears in Forlindon on Tolkien's early draft map for The Lord of the Rings. Christopher Tolkien cannot explain this feature and notes that in his own 1943 redrawn map, the circular area is no longer present. It is possible to create a collage of the Beleriand and the Eriador maps to show the small circular area on the Third Age map coinciding with the location of Amon Ereb. Noad suggests that Amon Ereb may have been once thought to have survived the submersion of Beleriand, although there is no textual evidence for it, and other Tolkienists such as Karen Fonstad have reconciled the two maps in a different way.