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|Head of State||King under the Mountain/King of Durin's folk|
|Location||North of Esgaroth, west of the Iron Hills|
|Formed from||Part of the exiled Dwarves of the Grey Mountains led by King Thrór|
 Founding and early history
With the awakening of Durin's Bane in the capital of Khazad-dûm, Thráin the Old, with those who would follow him, established residence in the Lonely Mountain in T.A. 1999. Under Thráin's rule the Arkenstone was discovered, and many riches were mined from its depths; After Thráin's death and his son Thorin I had ruled for ten years, he abandoned the Mountain in T.A. 2210 for the Grey Mountains; where his people were now gathering.
The mountain is speculated to have remained an active colony during this abandonment, yet its status as capital city was transferred to the Ered Mithrin. However in the later years they were involved in the War of the Dwarves and Dragons, and the Ered Mithrin was sacked by a Cold Drake. Grór, younger son of Dáin I, established a kindgom in the Iron Hills. Splitting from his brother, in T.A. 2590 the now king Thrór led a group back to the Lonely Mountain. Under Thrór's rule the Lonely Mountain once again became the capital of Durin's folk and they prospered.
It wasn't long before the great dragon Smaug heard of their great wealth, and one day decided to take their treasure for himself. In the year T.A. 2770 Smaug descended on the mountain in a ball of fire. He killed a large amount of the Dwarves living in the mountain. Most of the survivors fled to the Iron Hills, others went with the royal family into exile, and some may have simply went their own way.
The Lonely Mountain was empty for almost two hundred years, save the ever vigilant Smaug who slept in the inner most chamber on a great pile of wealth. But while Durin's folk wandered from the mountain to Dunland to the northern Blue Mountains, they ever longed for the halls of the Lonely Mountain.
 The Quest of Erebor and restoration
It wasn't until Thrór's grandson Thorin II Oakenshield met the Wizard Gandalf that the hopes of retaking the Lonely Mountain seemed possible. Indeed in the year T.A. 2941 with Gandalf's council, king Thorin and a small company of friends and family actually made it to the Lonely Mountain. After the Dragon Smaug had realized that the Dwarves had been helped by the Men of Dale he went to their town of Esgaroth intent on destroying them, only to be killed by a man named Bard. With the help of a Hobbit named Bilbo Baggins Thorin and company were able to retake the city and the treasure, therefore allowing Thorin to proclaim himself King under the Mountain. But after refusing to give any of the treasure to the Men of Esgaroth, and the Elves of Mirkwood, the mountain and the Dwarves and Hobbit in it were put under a bloodless siege.
Things nearly came to blows when Thorin's cousin Dáin Ironfoot (Grór's grandson) arrived as aid to his kinsman and nearly went to battle against the besiegers. But Gandalf interceded and warned them all of a great host of Orcs and Wargs coming to take the mountain. So the Elves, Men, and Dwarves made an alliance, and fought a bloody battle against their foes in the valley before the gate. In the end the defenders were victorious against the Orcs and Wargs, but king Thorin was mortally wounded and his nephews were both killed in the battle. After Thorin's death Dáin was made king of Durin's folk and of the mountain. Finally, after so many years of longing, the Longbeards could return to the Lonely Mountain.
 Prosperity and the War of the Ring
Under Dáin's rule the Dwarves of the Lonely Mountain became very rich and prosperous and the Lonely Mountain was restored to its original greatness.
Many years later, during the War of the Ring, conflict broke out between Dale and the East and eventually Men and Dwarves retreated into the mountain. King Brand and King Dáin were killed at its very gates. The Dwarves and Men held out for several days until word reached the ears of the Easterlings that the great hosts of Sauron in the south had been defeated in the Battle of the Morannon. With this news fear fell on the besiegers. When the besieged saw this they came forth from the Lonely Mountain, and attacked their enemy driving them from Dale across the Running.
Little is known of the reign of Thorin III Stonehelm, other than his people helping rebuild the cities of Gondor and the fortress of Helm's Deep, and part of his people moving to the Glittering Caves.
The Lonely Mountain was possibly 3,500 feet tall, as it was snowcapped at spring. Geologically, it was rich in metals and jewels.
The mountain was star-shaped with six ridges radiating as spurs from the peak.
The south-western spur contained Ravenhill housing a Dwarven guard-post. Between the two western spurs was a narrow vale which was the exit of the Back Door, behind an overhanging cliff. Rough steps ascended to the top of the southern ridge along a narrow ledge turning east behind a boulder into a steep bay.
Inside, the mountain was dug with passages and tunnels leading to cellars and halls and mansions such as the great chamber of Thrór near the Front Gate. A secret tunnel led to the "bottommost cellar"
The main entrance into the mountain was the Gate of Erebor on the south side, opening onto a valley between two great spurs of the mountain. At the end of the southwestern spur was Ravenhill, where there was a lookout post. The River Running sprang from beneath the mountain and issued from the Front Gate, forming a waterfall that fell into the valley below.
Inside the gate was a broad paved road that went alongside the river in a wide curve leading into the mountain. Not very far from the entrance was the Great Chamber of Thrór where feasts and councils were held.
In the Lower Halls, there was a vast chamber called the Great Hall of Thráin at the root of the mountain. From there a secret passageway led to a hidden door in the western side of the mountain. The Back Door was invisible from the outside except on Durin's Day, when the light of the setting sun would reveal the keyhole.
- J.R.R. Tolkien, The Hobbit, passim.
- J.R.R. Tolkien, The Fellowship of the Ring, Many Meetings
- J.R.R. Tolkien, The Fellowship of the Ring, The Council of Elrond
- J.R.R. Tolkien, The Return of the King, passim.
- J.R.R. Tolkien, The Lord of the Rings, Appendix A: III Durin's Folk
- J.R.R. Tolkien and Christopher Tolkien (ed.), Unfinished Tales, The Quest of Erebor
- J.R.R. Tolkien and Christopher Tolkien (ed.), The Peoples of Middle-earth