A Ruined Fortress Once Home to the Elves
“A dark power dwells in there, such as I have never felt before.
It is the shadow of an ancient horror. One that can summon the spirits of the dead. From out of the darkness,
a Necromancer has come!”
The Hobbit: AUJ Film
Dol Guldur was originally the capital of the Silvan Elves and was built upon a bald hill that was called Amon Lanc in Sindrin. Oropher eventually led his people north to the mountains in the far reaches of Greenwood the Great. Amon Lanc was abandoned and slowly the forest consumed all the lands around it.
Sometime after the end of the first Millennium of the Third Age, a shadow fell on the ancient ruins. Soon after, in the year 1050 the shadow began to spread throughout the Greenwood and the woodsman who dwelt along its western flank began to call it Mirkwood. The darkness spread and there were rumors of one called the Necromancer, who dwelt there in the old ruins and practiced dark magic. Soon after, it became know as Dol Guldur, the Hill of Sorcery.
Thranduil son of Oropher led his people over the Forest River, where they remained ever vigilant to the growing evil in the south.
Some believe that in the year 2092 of the Third Age, the Necromancer who was in truth Sauron, intended to claim the Lonely Mountain for his his own. His intention was to seduce the dragon Smaug into his service and use the worms great fire to terrible effect in the assault upon Middle-earth, long planned by the Dark Lord. The Mountain would become a stronghold of evil and along with Mount Gundabad and the resurrection of Carn Dûm, the North of Middle-earth would be his to command.
However, other forces were also at work and a small company of dwarves returned through great danger to the Mountain, led by Thorin Oakenshield. Their presence was a catalyst in the death of the dragon and though Sauron sent forces there to take the treasure, the battle for Erebor was lost. When the White Council set themselves against Dol Guldur, Sauron fled in secret to Mordor, where his servants the Nazgûl had long prepared his return!
Dol Guldur was a place of great evil and Sauron had made of it a fortress of Shadow.
Only long after was it learned that Thráin had been taken alive and brought to the pits of Dol Guldur. There he was tormented and the Ring taken from him, and there at last he died.
From The Lord of the Rings in ‘Appendix A ~ III Durin’s Folk’
Many tales were told to those that gathered in the Council of Elrond and Gandalf’s not the least of these.
Some here will remember that many years ago I myself dared to pass the doors of the Necromancer in Dol Guldur, and secretly I explored his ways, and found thus that our fears were true: he was non other than Sauron, our Enemy of old, at length taking shape and power again. Some, too, will remember also that Saruman dissuaded us from open deed against him and for long we watched him only. Yet at last, as his shadow grew, Saruman yielded and the Council put forth it’s strength and drove the evil out of Mirkwood ~ and the was in the very year of the finding of this Ring: a strange chance, if chance it was.
From The Lord of the Rings in the chapter ‘The Council of Elrond’
Gandalf: There is something at work beyond the evil of Smaug. Something far more powerful. We could remain blind to it but it will not be ignoring us, that I can promise you. A sickness lies over the Greenwood. The Woodsmen who live there now call it Mirkwood and, uh, they say…
Saruman: Well, don’t stop now. Tell us what the Woodsmen say.
Gandalf: They speak of a Necromancer living in Dol Guldur, a sorcerer who could summon the dead.
Saruman: That’s absurd. No such power exists in this world. This “Necromancer” is nothing more than a mortal man, a conjurer dabbling in black magic.
From The Hobbit: An Unexpected Journey in the scene ‘The White Council’