FAQ / What is the difference between Udûn Angband and Utumno

Utumno was Morgoth's ancient fortress in the times of the Lamps of the Valar.

Now Melkor began the delving and building of a vast fortress, deep under Earth, beneath dark mountains where the beams of Illuin were cold and dim. That stronghold was named Utumno. And though the Valar knew naught of it as yet, nonetheless the evil of Melkor and the blight of his hatred flowed out thence, and the Spring of Arda was marred. Green things fell sick and rotted, and rivers were choked with weeds and slime, and fens were made, rank and poisonous, the breeding place of flies; and forests grew dark and perilous, the haunts of fear; and beasts became monsters of horn and ivory and dyed the earth with blood. The Silmarillion: Of The Beginning Of Days

It was destroyed though, when the Valar attacked Melkor at the time of the Awakening of the Firstborn.

Long and grievous was the siege of Utumno, and many battles were fought before its gates of which naught but the rumour is known to the Elves... ...But at the last the gates of Utumno were broken and the halls unroofed, and Melkor took refuge in the uttermost pit. The Silmarillion: Of The Coming Of The Elves And The Captivity of Melkor

Udûn is the Sindarion form of Utumno.

`You cannot pass,' he said. The orcs stood still, and a dead silence fell. `I am a servant of the Secret Fire, wielder of the flame of Anor. You cannot pass. The dark fire will not avail you, flame of Udûn. Go back to the Shadow! You cannot pass.' The Fellowship of the Ring: The Bridge Of Khazad-dûm

turn: 'valley' in Tumhalad, Tumladen; Quenya tumbo (cf. Treebeard's tumbalemorna 'lack deep valley'. The Two Towers III 4). Cf. Utumno, Sindarin Udûn (Gandalf in Mordor named the Balrog 'Flame of Udûn'), a name afterwards used of the deep dale in Moria between the Morannon and the Isenmouths. The Silmarillion: Appendix

Angband was an outlying fortress built to protect Utumno from any attacks by the Valar.

And Melkor made also a fortress and armoury not far from the north-western shores of the sea, to resist any assault that might come from Aman. That stronghold was commanded by Sauron, lieutenant of Melkor; and it was named Angband. The Silmarillion: Of The Coming Of The Elves And The Captivity Of Melkor

When Utumno was ruined, Angband was not completely destroyed, and once Melkor returned to Middle-earth, he chose it as his new capital.

Far beneath the rained halls of Angband, in vaults to which the Valar in the haste of their assault had not descended, Balrogs lurked still, awaiting ever the return of their Lord. The Silmarillion: Of The Flight Of The Noldor

Angband was eventually destroyed in the War of Wrath by the Valar.

Thus an end was made of the power of Angband in the North, and' the evil realm was brought to naught. The Silmarillion: Of The Voyage Of Eärendil And The War Of Wrath

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