Why did Sauron specifically choose Mount Doom?

Question

This follows on from my previous question about Mordor.

What was so special about Mount Doom for Sauron to decide to use this place to forge the One Ring? I am under the impression that Mount Doom was more than just a volcano (or Mountain of Fire, as it's never explicitly called a volcano).

This thread suggests that Mount Doom was the only volcano/mountain of fire in Middle Earth. Is this true? Is there anything that backs up this claim?

I am assuming that Mount Doom was already in place before Sauron decided to settle in Mordor. For Sauron it may have been the deciding factor in selecting his new home, as it was where he forged the Ring of Power.

This answer states that Mount Doom had magical significance, but I struggle to find any explanation or source of this significance.

Was there any connection between Mount Doom and Utumno, Angband or Morgoth himself?

This answer suggests that "volcanoes were remainders of the doings of Melkor (Morgoth) in his attempts to undo the work of the Valar in the days before the reckoning of time". So if Morgoth was responsible for all volcanoes, what made Mount Doom so special?

As a child I was under the impression that Morgoth's final resting place was Mount Doom, and hence its special significance. But researching into this as an adult I can find no reference to this happening, so I'm not sure where I got this idea from.

Answer 1

Sauron definitely chose Mordor because of Mount Doom:

[T]here was a fiery mountain in that land that the Elves named Orodruin. Indeed for that reason Sauron had set there his dwelling long before, for he used the fire that welled there from the heart of the earth in his sorceries and in his forging

^{The Silmarillion V Of the Rings of Power and the Third Age}

We aren't told exactly what it is about Orodruin that was so attractive to Sauron, but it does have several desirable properties:

• It's active, which is helpful

• It's, y'know, there. Volcanoes are very rare in Tolkien's mythology; Orodruin is the only one confirmed, and Thangorodrim is often believed to have been one¹ largely because of this passage:

  Fingon looked towards Thangorodrim, and there was a dark cloud about it, and a black smoke went up; and he knew that the wrath of Morgoth was aroused

  ^{The Silmarillion III Quenta Silmarillion Chapter 20: "Of the Fifth Battle: Nirnaeth Arnoediad"}

  So the fact that it exists at all is a point in its favour

• It's quite far from his enemies, who live almost exclusively on the western edge of the continent, as you can see from the map below:

  

  Notable landmarks are:

  • Orodruin, circled in red
  • Lindon, where basically all of the Noldor live in the early Second Age², circled in blue
  • Númenor and the Undying Lands, not pictured but in the direction of that big green arrow

• It's quite near his allies (or potential future allies): the Easterlings of Rhûn and Southrons of Harad

If there was any especially magical factor distinguishing Orodruin, Tolkien does not discuss it.

---

¹ It's sometimes speculated, based on geographic factors, that Erebor was also a volcano, albeit a dormant one, but this is unconfirmed

² The two most easterly Noldorin strongholds (Rivendell and Eregion) wouldn't be established until well into the Second Age (SA 1697 and 700/750, respectively). Lothlórien had been established long before, but was founded by the lesser Silvan elves; it wouldn't come under Noldorin leadership until the Third Age

Answer 2

Mount Doom is the only place where the One Ring can be made or unmade

When I wrote this answer, the title of the question was "What was special about Mount Doom". It has since been changed to "Why did Sauron specifically choose Mount Doom". The new title may well represent what the OP wanted to ask, but my answer is about what makes Mount Doom special (at the time of "The Lord of the Rings"). Sauron may well have chosen it for essentially same reason: that it was the only place that the One Ring could be made or unmade.

We can't be sure that it was the only volcano in Middle-earth, but it is the one that houses the Cracks of Doom: the place where the One Ring was made, and the only place that it can be unmade.

The Ring was unbreakable by any smithcraft less than his own. It was indissoluble in any fire, save the undying subterranean fire where it was made – and that was unapproachable, in Mordor.

_{The Letters of JRR Tolkien Letter 131}

In "The Shadow of the Past", Galdalf tells Frodo that

‘Your small fire, of course, would not melt even ordinary gold. This Ring has already passed through it unscathed, and even unheated. But there is no smith’s forge in this Shire that could change it at all. Not even the anvils and furnaces of the Dwarves could do that. It has been said that dragon-fire could melt and consume the Rings of Power, but there is not now any dragon left on earth in which the old fire is hot enough; nor was there ever any dragon, not even Ancalagon the Black, who could have harmed the One Ring, the Ruling Ring, for that was made by Sauron himself.

‘There is only one way: to find the Cracks of Doom in the depths of Orodruin, the Fire-mountain, and cast the Ring in there, if you really wish to destroy it, to put it beyond the grasp of the Enemy for ever.’

_{The Lord of the Rings Book One, Chapter 2 The Shadow of the Past}

Either the fire in the Cracks of Doom is hotter than any other fire on Middle-Earth, or it has special power because it was where the One Ring was made. Either way, what makes Mount Doom special is that it is the only place where the Ring and be unmade.