The Lonely Mountain
The Lonely Mountain or Erebor is a mountain in the northeast of Rhovanion. It is also the source of the River Running (Celduin). For many ages of Middle-earth, it had been inhabited by the Dwarves of Durin's Folk or Longbeards -- up until the latter half of the Third Age and now again in its closing years.
Years of the Trees and First Age
It is known that the Dwarves of Durin's Folk discovered the mineral wealth of the Lonely Mountain sometime after the awakening of the first Durin. A mining colony was soon set up and a road was laid out to connect the dwarves to their great cities from the Iron Hills and as far west as their realms and possessions in the Blue Mountians.
Second and Third Ages
The Dwarves probably still lived and mined in the Mountain during the Second Age but it wasn't until the mid-Third Age that the colony had become a firmly established Kingdom of the Dwarves. After the fall of the ancient Kingdom of Khazad-dûm due to the awakening of the Balrog Durin's Bane in TA 1981, the survivors under Thráin I followed him to the Lonely Mountain and the colony became the ancestral home of the King under the Mountain by TA 1999, it became a Dwarven stronghold, where the dwarves became a numerous and prosperous people. In this time, the dwarves got very rich, amassed a large amount of gold, and treasure which included the famous jewel known as the Arkenstone. For two-hundred and eleven years, the kingdom prospered and endured until Thorin I abandoned it to join his kin in the Grey Mountains (Ered Mithrin) where they began to live, and the Lonely Mountain was abandoned for three-hundred and eighty years. However, the Dwarves of the Grey Mountains began experiencing attacks by the dragons that still lived in those mountains and became embroiled in a costly war against them, which forced them to abandon the Grey Mountains in TA 2590. The dwarves went their separate ways with Grór and his followers settling in the Iron Hills and Thrór and his followers settling in Lonely Mountain.
The Lonely Mountain again became a Dwarven Kingdom of greater prestige then before with the Dwarves of that time becoming highly skilled in masonry and stonework, and there was great demand for their work by the surrounding peoples. The Men of Rhovanion established Dale and established a very close trade and culture relationship with the Dwarves of the Mountain, and men and their sons were eager to learn their skills. Unfortunately, it was this prosperity that attracted Smaug to the Mountain.
Whilst Thorin Oakenshield was out hunting one day in TA 2770, Smaug came from the Mountains as a young dragon and took over the Mountain, hoarding all the gold. Thráin II and several companions escaped by (as was later discovered) a secret door. For many years, the dwarves lived in exile in the Blue Mountians until, by a chance meeting, Gandalf the Grey met Thorin Oakenshield and they planned to reclaim the Mountain. This is told in detail in The Quest of Erebor.
In TA 2941, Bilbo Baggins and Thorin's company travelled to the Lonely Mountain to regain the treasure Smaug had stolen. Set into the side of the Mountain was a secret door, five feet high and wide enough for three to walk abreast. Gandalf had managed to obtain the door's key, which would only open it when the setting sun and the last moon of autumn were in the sky together. By a fortunate coincidence, this happened just as Bilbo and the Dwarves arrived.
Smaug was eventually slain -- shot out of the sky with a well-aimed arrow to his only weak spot by Bard the Bowman, a man of Esgaroth or Laketown -- and Thorin claimed the Mountain. Bard later became king of the area in the shadow of the Lonely Mountain, known as Dale. However, Elves of Mirkwood and Men of Esgaroth claimed a part of the treasure, which Thorin refused to share. This led to the Battle of Five Armies, where Dáin II Ironfoot came to the aid of his cousin Thorin, but Dwarves, Elves, and Men joined ranks together with the Eagles against the orcs. During the battle, Thorin was mortally injured and the titles King under the Mountain and King of Durin's Folk passed to Dáin.
