Attack on Dol Guldur

The Attack on Dol Guldur was an expedition launched by the White Council in TA 2941 of the Third Age against the fortress of Dol Guldur in southern Mirkwood.

Prelude
The old fortress of Dol Guldur was established in the year TA 1000, which followed the return of the Dark Lord Sauron in Middle-earth. However, Sauron hid his identity disguised himself as the Necromancer of Dol Guldur. Dol Guldur was originally known as Amon Lanc ("Bald Hill"), and had been the capital of Oropher's Silvan Elves, who had departed north to the Dark Mountains (later known as the Mountains of Mirkwood). After Sauron took over Amon Lanc, Thranduil, son of Oropher, led his people over the Forest River, where they remained for hundreds of years.

The Council of the Wise long feared the Necromancer might indeed be Sauron, and in the year TA 2063, Gandalf, one of the Five Wizards, went to Dol Guldur to investigate, but Sauron, who was not yet powerful, fled to the East before the Wizard could find out the truth. During the Watchful Peace, Sauron returned to Dol Guldur in the year TA 2460, the same year as the One Ring was found by Sméagol. However, the Ring disappeared with Sméagol under the Misty Mountains.

In TA 2845, Thráin II, son of Thrór, King of Durin's Folk, and holder of the last of the Seven Rings of the Dwarves, was imprisoned in Dol Guldur's dungeons. Five years later, Gandalf returned to Dol Guldur, finding the dying Thráin, and Gandalf was entrusted with the map and key to give to Thorin II, although Thráin could not tell him his own or his son's name before he died. After Thráin's death, Gandalf confirmed that Sauron was the master of Dol Guldur at that time.

Gandalf returned to the White Council and urged an attack on Dol Guldur, but was overruled by Saruman, who had begun searching for the One Ring in the area by then. In TA 2941, Saruman finally agreed to an attack, which occurred at the same time as the Quest of Erebor. This was carefully planned by Gandalf, so that Sauron and Smaug could not assist each other.

The Attack
Not much is known of the actual battle (if this was simply a duel between great powers, or if it involved the use of armies of any kind) besides that the White Council marched against the great fortress, and that Sauron fled to Mordor, his plans now ready.

Aftermath
It is unclear if the Council actually ever entered the fortress because Dol Guldur remained staffed by the lieutenant of Barad-dûr, and later Khamûl until the fortress's destruction during the War of the Ring. With victory theirs, Gandalf immediately left for Erebor, where he would take part in the Battle of the Five Armies.

Portrayal and adaption
The Attack on Dol Guldur appears in The Hobbit: The Battle of the Five Armies as one of the main plots, besides Smaug's attack to Esgaroth and the gathering for battle at Erebor. Considering Tolkien did not write much about these events in Dol Guldur, Jackson had the right to take creative liberties in a completely justified context. After Gandalf was defeated and captured after facing Sauron in Desolation of Smaug, the White Council (Galadriel, Saruman and Elrond) came to his aid and faced Sauron/Necromancer and The Nine (Nazgûl).

According to the Official Movie Guide to BOFA, In coming to Gandalf’s aid, Galadriel has to grapple with the seductive power of the Necromancer to draw other beings into a void of darkness, despair and decay. She has to summon every particle of her strength to resist and, in doing so, we see Galadriel’s incredible power and realize that — but for the finesse and strength of her spirit — how quickly power for goodness could be turned to evil.” Blanchett also says Galadriel “uses the language of the enemy.”

It is expected that The Three Guardians of the Elven Rings run into some kind of fight with the Nazgûl. Galadriel and Saruman, until now, are expected to have an intense confrontation with Sauron.