Erebor

Erebor, also known as the Lonely Mountain, is a dwarven kingdom in Tolkien's Middle-earth. It lies to the east of the Misty Mountains, overlooking the valley of Dale and the Long Lake, with the massive Lonely Mountain as its central feature. The realm was founded by Durin I of Durin's Folk and became the chief stronghold of the Dwarves of the North, known for its vast wealth derived from gold and gems mined within the mountain. The halls beneath the peak—the King Under the Mountain's throne room and the vast treasure vaults—formed a formidable fortress and a cultural heart of Durin's line.

During the later years of the Third Age, Erebor was attacked by the dragon Smaug, who drove its dwarves into exile and devastated Dale. In the centuries that followed, the kingdom's wealth remained in Smaug's hoard until the events recounted in The Hobbit, when Thorin Oakenshield and a company of companions reclaimed Erebor with the aid of Bilbo Baggins. Smaug was slain by Bard the Bowman, and the adjacent field became the site of the Battle of the Five Armies. After the conflict, the dwarves restored their kingdom and Thorin briefly reigned before dying; the throne eventually passed to Dáin II Ironfoot.

Following the War of the Ring, Erebor continued as the principal realm of Durin's Folk, and Dale was rebuilt near the mountain's base. Erebor's reclamation restored a major source of dwarven craft and trade in the northern regions of Middle-earth. The Arkenstone, a legendary gem within the king's hoard, symbolized kingship and the mountain's wealth, though its possession became a point of contention during the reclaiming.