Battles of Lórien and invasion of eastern Rohan

The Battle of Lothlórien (never given a proper name in the text) is a fictional event during the War of the Ring in J. R. R. Tolkien's The Lord of the Rings. It is an encounter between the Orcs of Dol Guldur and Mordor against the Galadhrim of Lothlórien under Galadriel. The battle was one of the largest of the war and the victory of the Elves allowed Celeborn to lead an assault on Dol Guldur, where Galadriel ended the evil influence of Sauron in Mirkwood.

It is unknown how the Orc army crossed the River Anduin, though the North Undeep seems the most likely place to ford. Forces from Dol Guldur, reinforced with Orcs from Mordor assaulted Lothlórien three times, assisted at least once in a joint attack from the west by the Goblins of Moria. Though the battles are not described in detail by Tolkien, the fair woods of the borders of Lothlórien suffered griveous harm by fire, though the valour of the Elves prevented the enemy from penetrating too deeply into their forest realm. Thrice the enemy attacked, and the three times the assaults were driven back.

The valour of the Elven people that lived in Lórien was great, but Tolkien states that the main reason why Lórien was not conquered was "the power that dwelt there was far too great for any to overcome, save if Sauron had come there himself". Such power was the Lady Galadriel, wearing Nenya, who was able to defeat the Orcs; who then fled south towards into Fangorn Forest. Treebeard and a host of Ents, having already laid ruin to Isengard some days before set out to prevent them entering Rohan. The despairing Orcs fled eastward but were either killed by the tree-shepherds or drowned in the River Anduin.

Aftermath
Following the battle, Celeborn and Galadriel led the Galadhrim across the Anduin in a fleet of many small elf boats. They entered Mirkwood and attacked Dol Guldur. Then, Galadriel came forth and threw down the walls and cleansed its pits with her power, and ended the grasp of evil in the forest. As news of the victory of King Elessar down south reached the Wood Elves, Thranduil (who had recently defeated an army in the Battle of Mirkwood) met with Celeborn on April 6.

Mirkwood was divided between Thranduil (who claimed the North), the Beornings (who settled in the middle, the 'Narrows') and Celeborn who added the southern half to his realm, renaming it 'Eastern Lórien'. Despite these victories, the Elves began to dwindle and Celeborn himself departed over the Sea during the Fourth Age.