The underground Dwarven city called Moria is named Khazad-dûm in J.R.R. Tolkien’s legendarium.
Khazad-dûm means “Dwarrowdelve” in Tolkien’s rendering of the Dwarven language. It was built beneath the Misty Mountains and became the greatest realm of the Dwarves, famous for its wealth and its mines of mithril.
The Dwarves awakened a Balrog while mining for mithril, and the creature killed King Durin VI. After this disaster, the Dwarves abandoned the city, which became known as Moria, a Sindarin name associated with darkness.
In The Lord of the Rings, the Fellowship travels through the abandoned halls and encounters the Balrog. Erebor is another Dwarven kingdom, the Lonely Mountain, while Belegost is an older city of the Blue Mountains.