Also called Orodruin, the Fiery Mountain and Mountain of Fire.

An active volcano located in Mordor on the Plateau of Gorgoroth, rising about 3000 feet above the plateau. On its slopes Sauron had constructed a road that lead from Barad-dûr and rose, circling the mountain, until it reached the Sammath Naur, Sauron's Chambers of Fire.

In SA 1600, in forges constructed in the Sammath Naur, Sauron used the fires of Mount Doom to forge the One Ring. With this Ring, he hoped to control the Rings of Power that had been forged by the Elves of Eregion with Sauron's help.

On March 25 of TA 3019 Frodo reached Sammath Naur intending to cast the One Ring back into the Cracks of Doom and destroy it. However, he did not have the strength to resist the power of the Ring, and put it on his finger instead. He was then attacked by Gollum who bit the ring from his finger and then lost his balance and fell into the Cracks of Doom. The Ring was thus destroyed and Sauron disappeared into shadow, never to reappear.
Encyclopedia entry originally written by PotbellyHairyfoot