Dorthonion
Dorthonion (Sindarin for "Land of Pines") was a highland region of northern Beleriand during the First Age. It was held by the Noldor following their return to Middle-earth, and was chiefly the realm of the brothers Angrod and Aegnor.
Dorthonion lay to the south of the Thangorodrim and formed part of the defensive cordon around Angband during the Siege of Angband. Its land was high, cold, and mountainous, covered with dense forests of pine. The region was strategically important, standing above the plains of Ard-galen to the south, and was therefore heavily fortified by the Noldor during the Long Peace.
After the return of the Noldor, Dorthonion was granted by High King Fingolfin to his nephews Angrod and Aegnor, brothers of Finrod Felagund and Galadriel. They made their halls upon the northern slopes and ruled the highlands jointly.
During the Glorious Battle (Dagor Aglareb), Morgoth's forces attempted to invade Beleriand through Dorthonion, but were driven back by the Noldor. For centuries thereafter, Dorthonion remained an important stronghold in the north.
This ended with the Battle of Sudden Flame (Dagor Bragollach) in F.A. 455, when Morgoth loosed rivers of fire from the Thangorodrim. Much of Ard-galen was burned away, and the flames reached into Dorthonion itself. Morgoth’s forces swept southward, overrunning the highlands. Both Angrod and Aegnor were slain in the battle, and Dorthonion fell under the control of Orcs.
In the aftermath, the region was corrupted and became known as Taur-nu-Fuin ("Forest under Nightshade"). It was a place of terror, haunted by creatures of Morgoth, and few of the Free Peoples ventured there. Barahir and his outlaw band hid in Dorthonion for a time after the battle, but most of its Elven population was destroyed or driven out.
Dorthonion's fall was a turning point in the wars of Beleriand, as it deprived the Noldor of one of their northern bulwarks and left the lands further south vulnerable to Morgoth’s assaults. Its transformation into Taur-nu-Fuin was remembered as one of the great tragedies of the First Age.