§ Of Beleriand and Its Realms The Silmarillion

South of Ard-galen the great highland named Dorthonion stretched for sixty leagues from west to east; great pine forests it bore, especially on its northern and western sides. By gentle slopes from the 'plain it rose to a bleak and lofty land, where lay many tarns at the feet of bare tors whose heads were higher than the peaks of Ered Wethrin; but southward where it looked towards Doriath it fell suddenly in dreadful precipices. From the northern slopes of Dorthonion Angrod and Aegnor, sons of Finarfin, looked out over the fields of Ard-galen, and were the vassals of their brother Finrod, lord of Nargothrond; their people were few, for the land was barren, and the great highlands behind were deemed to be a bulwark that Morgoth would not lightly seek to cross.