The Lonely Mountain.

The Lonely Mountain was lying in Erebor East of Mirkwood and West of the Iron Hills, South of Ered Mithrin and Withered Heath. The Kingdom under the Mountain was founded in Third age year1999 by Thrain I. after the Dwarves had abandoned Moria in Hithaeglir because of the Balrog. The size of the mountain was about 10 Miles in diameter and it was high enough to be snowcapped at spring ( 3500 feet ? ) and its peak pierced the clouds. There were six spurs radiating from the central peak and in the broad Southernmost vale was the city of Dale. Before Smaug descented and ruined Dale and the dwarf-kingdom the mountain had been clad in threes River Celduin had its spring at the Lonely Mountain inside the front gate to the halls inside the mountain.

The Dwarves digged and delved into the mountain and made tunnels and corridors, chambers and archways and in the middle was made the Great Hall. In their efforts they digged gold, silver and gems out of the mountain but among them all the greatest was the Arkenstone.

Thorin I. Left the mountain in 2210. It is not told why. The king; his father, was dead 20 years before so it seems a little strange that the new King should abandon his Kingdom just like that. But for whatever reason the dwarves left and went North to Ered Mithrin and nothing is told of the Kingdom before Thror four generations later returned to Erebor and the Mountain in Third age year 2590.

Thror gathered great wealth and had the friendship of all that dwelt near, the people of Dale, the Elves of Mirkwood and the beast and birds of the land but Smaug the Golden heard rumours of his happiness and wealth and he descended in the year Third age 2770 upon the mountain and destroyed the whole region and entered the deep halls of the Dwarves in flames but Thror escape with his son Thrain II. and Thorin II. his grandson through a secret intrance in the West of the mountain. In the wrath of Smaugs it is quite possible he ruined Esgaroth in the Long Lake for the first time.

Story of Hobbit.

Battle of Five Armies 2941. Thorin II. dies but the kingdom regained and Dain II. becomes the new king.