The most ancient and famous of all the Dwarf kingdoms was Khazad-dûm, renamed Moria in the Second Age during the War of the Last Alliance when the Dwarves closed the doors of their Kingdom to the world.

It was founded by Durin the Deathless, a great dwarf-lord. It was a kingdom, and a mine, and it went through the Misty Mountains so a traveller could pass easily from one side to the other. The dwarves of Khazad-dûm were friends with the elves that lived near the west entrance. Their leader, Celebrimbor, helped to build the great west gate that survived into the Third Age (the West-gate of Moria). This friendship ended in 1697 of the Second Age and the coming of Sauron to Eregion.

They mined mainly mithril in Khazad-dûm, and they mined very deep, because it was valuable. But in the year 1980 of the Third Age the Dwarves delved too deep beneath Mount Barazinbar and an entombed Balrog was released within the halls of Khazad-dûm. So terrible was the Balrog's strength and wrath that the Dwarves were either slain or driven from their Kingdom. It was then that the mine aquired the name Moria, meaning 'black pit'.

It was briefly reclaimed in 2989 of the Third Age by Balin and some of his kin from Erebor, but they were eventually defeated.

When the Fellowship of the Ring entered the mine in the Third Age it was a chasm of darkness that had long been abandoned by the Dwarves. Its treasures had been stripped by hordes of orcs, and through is barren corridors there still walked the Balrog and many bands of Orcs and Trolls.

However, the reign of the Balrog ended when Gandalf finally overcame the monster and threw it from the top of Durins Tower on the high peak of Zirak-zigil.