|Location||Between Beleriand and Eriador|
|Realms||Belegost, Nogrod, and later realms like Thorin's Halls|
|Inhabitants||Dwarves (Broadbeams, Firebeards, and Longbeards)|
|Description||Great western mountain range|
|Other names||Ered Luin, Ered Lindon|
|Events||War of Wrath|
|References||The Fellowship of the Ring, Quest of Erebor, The Silmarillion|
In the Beginning
During the creation of Arda, the Blue Mountains were meant to line up directly with the Grey Mountains of the southlands, forming the western wall of Arda. They lay parallel to the Red Mountains and Yellow Mountains that formed the eastern wall. The Blue Mountains were originally connected with the Red Mountains by the Iron Mountains which stretched across the entire north. The symmetry of Arda was broken during the wars between the Valar and Melkor in the ages before the Years of the Lamps.
Before and During the First Age
In the First Age, the Blue Mountains were an unbroken line separating Eriador from Beleriand. Seven rivers flowed from its western side, and the land these rivers flowed through was known as Ossiriand. Later, when the Green-elves settled there, the land was called Lindon, and the mountains sometimes referred to as the Ered Lindon.
The Second Age
The Blue Mountains were ruined during the War of Wrath, and in the south central end of the range the sea broke through. The River Lhûn now flowed through the mountains to the Gulf of Lhûn. On the western side a small section of Lindon remained, and here the retreating Elves built Kingdom of Lindon, ruled by Ereinion Gil-galad, last High King of the Noldor. Its most important city was the Grey Havens, from where departing Elves left Middle-earth for Valinor. Also located here were the two regions of Forlindon to the North, with its chief port being Forlond. And Harlindon to the South, which Harlond was its chief port.
The Dwarven cities of Nogrod and Belegost were also ruined when the mountains were broken. Most of the Dwarves migrated east to Khazad-dûm. However some remained to rebuild. Overtime however, the Dwarves seemed to have largely moved to the Southern chain.
The Third AgeDurin's folk who were exiled from their halls in Erebor by Smaug the Dragon. After the War of the Dwarves and Orcs, King Thrain II established his throne in the Northern chain beyond the Little Lune river and later his son Thorin Oakenshield ruled after he went missing. During Thorin's reign many of the wandering Longbeards joined him and they became prosperous in a fashion. However Erebor was retaken from Smaug by Thorin and company in 2941, and many if not most of Durin's folk relocated there.