This article is about the fictional underground city. For other meanings of "Moria," see Moria.

In J. R. R. Tolkien's fictional world, Middle-earth, Moria (also known as Khazad-dûm, The Black Chasm, The Black Pit, Dwarrowdelf, Hadhodrond, and Phurunargian) is the name given to the underground city, mines, and connected tunnels that run through the central Misty Mountains. There, for many thousands of years, a thriving Dwarvish community created the greatest city ever known.

The city was founded by Durin the Deathless long before the First Age of the Sun, during the 'Ages of Stars'. Durin woke at Mount Gundabad in the Misty Mountains. Travelling south he came to a lake, where he saw a crown glittering in the deep. This lake, called Mirrormere or Kheled-zaram, was later a revered place among Dwarves. Nearby, Durin first began his city, which was called Khazad-dûm by the Dwarves and also Dwarrowdelf by Men and Hadhodrond by Elves.

Durin the Deathless thus became King Durin I of Khazad-dûm. Afterwards, other rulers of Khazad-dûm were sometimes named Durin, reincarnations of Durin I, who the dwarves believed came to live again among his people.

In the Second Age, the Dwarves of Khazad-dûm forged a friendship with the Ñoldorin Elf realm of Eregion — but this friendship ended in disaster with the forging of the Rings of Power, the rise of Sauron wielding the One Ring, and the destruction of the Elven realm. Then Khazad-dûm was closed, and Sauron could not enter it.

In the year 1980 of the Third Age, however, the Dwarves, seeking a precious metal called mithril, delved too deep and awakened Durin's Bane, an evil fire spirit from the elder days. This spirit fought the Dwarves and killed Durin VI, the King of Khazad-dûm. The following year, it also killed Náin, Durin VI's son, and the Dwarves were forced to flee their ancient home. After that, the realm was known as Moria, the Black Pit. (However, it may be worth noting that the dwarves might not have been at fault, since it is the same year the Nazgul re-awakened to the summons of the Dark Lord).

Eventually, Sauron began to people the Pit with his followers, mainly orcs and trolls, and they discovered that the terror was, in fact, a Balrog of Morgoth. In 2799 of the Third Age, the Battle of Azanulbizar was fought on Moria's East Gate, and the Dwarves were successful in driving away Sauron's minions, but they would not enter for fear of the Balrog. Several Dwarven generations later, Balin, who had accompanied Bilbo Baggins on the Quest of Erebor described in The Hobbit, led a new group of Dwarves to reopen the city. At first all went well, but after a few years the community was destroyed by Orcs and similar creatures, although their fate was initially unknown.

By the end of the Third Age, at the time of the events of The Lord of the Rings, Moria had become a dark and cursed place. In The Lord of the Rings, when Frodo Baggins set out from Rivendell with the Fellowship, they at first planned to travel over the Misty Mountains. When they were stopped by snow on Mt. Caradhras, they found themselves pursued by wolves and Orcs, and fled into Moria, so as to go under the mountains. There they found Balin's journal and learned the fate of his expedition. They were then set upon by a host of trolls, Orcs, and the Balrog. Gandalf fought the Balrog on a narrow bridge and succeeded in destroying a section of bridge to make the Balrog fall. As it fell, the Balrog snagged Gandalf's leg with its whip of thongs and pulled him after it, sending them both plunging into the abyss spanned by the bridge. The rest of the Fellowship managed to escape Moria and reach Lothlórien mostly unharmed.

Unknown to the Fellowship, both Gandalf and the Balrog survived the fall and fought a ferocious battle from the depths of Moria to the mountains above, demolishing the top of the legendary Dimrill Stair and a part of the surrounding mountain peak in the process. Gandalf cast down the Balrog upon the mountainside and lived just long enough to see it die, but his story was not yet ended. (See Gandalf's entry for further details.)

While Gandalf had felled the Balrog and some of the orcs of Moria died in the War of the Ring, Moria remained a place of evil creatures.

It is told however that Durin VII and Last may have re-founded Moria, and retrieved what he could of his people's once-mighty riches, but many Dwarves seem to have remained at the Iron Hills, Aglarond, and the refounded Kingdom under the mountain at Erebor. However, considering the Dwarvish love of Mithril and their longing for their ancient homeland, it is more than likely that Durin's folk dwelt once again beneath the Mountains of Moria in Khazad-dûm.