Rivendell was founded in SA (Second Age) 1697 almost 4,500 years before the War of the Ring by Elrond, the son of Eärendil and Elwing. Many momentous events led up to the founding of Rivendell, which are told here in brief.

The Gwaith-i-Mírdain, ‘People of the Jewel-smiths’, built a fair city west of Moria’s west gate early in the Second Age and it was here that Celebrimbor forged the Elven-rings. Alas, for the Mírdain jewel-smiths were ever-eager to increase their skill. When Sauron came to their gates in the form of Annatar (‘Gift-lord’) they welcomed him and embraced his teachings, for in those times his knowledge was great and he remained fair-seeming to all but Círdan and Gil-galad of the Grey Havens. In the years that followed the jewel-smiths grew mighty in their skills and gave thought to the making of rings of power. But their skills were fostered by Annatar, and their designs sullied by Sauron’s enchantments.

Celebrimbor forged the Three Elven-rings alone, and they were untouched by Sauron, but alas! all rings were subject to the dominance of the One that Sauron forged in the fires of Barad-dûr. This was Sauron’s grand design to enslave the free peoples, Men, Elves and Dwarves. But Celebrimbor, when he placed the rings on his fingers, perceived Sauron’s iniquity and heard the song of binding. Celebrimbor removed the Elven-rings and hid them.

Sauron was enraged that the Elves had failed to be snared by his treachery, and returned with an army to the gates of the city of the Gwaith-i-Mírdain demanding that all the rings be given over, as they were made with his teachings. When Celebrimbor refused to give up the Three, Sauron unleashed war against him and destroyed the city of Eregion. Elrond had been sent by Gil-galad from the Grey Havens to Eregion, to aid in the defense of that realm against Sauron. When the city fell, Elrond and many of the surviving Noldor fled northwards to found the vale of Rivendell.

Rivendell was defended by its natural position and the river itself, which by Elven-enchantment would rise up by to drive away enemies attempting to ford. Thus it resisted Sauron’s attacks in the Second Age until Gil-galad and a host of Númenoreans drove Sauron’s forces from Eriador.

At the end of the Second Age the Last Alliance rode forth from Rivendell with Elrond as the herald of Gil-galad. With Círdan he stood beside the High-King of the Elves in his mortal combat with Sauron before Barad-dûr, and when Isildur took the One Ring he counselled fruitlessly that it should be destroyed.

In the Third Age Rivendell remained as the home of many Elven lords and ladies, a place where wise counsel could be found and the weariness of the mortal world forgotten.

Elrond had been entrusted with Vilya, the Ring of Sapphire that had been given to Gil-galad by Celebrimbor. With the loss of the One Ring Elrond began to use Vilya, the mightiest of the Three, to protect Rivendell during the wars of the Third Age - notably around 1375 when Rivendell was besieged by the Witch-king of Angmar and his forces. As with Lothlórien, the power of the Ring lent Rivendell an air of timelessness that tempered the sadness of Middle-earth and was a reminder to the Eldar of the peace of the deathless lands.

Elrond’s wife Celebrían, daughter of Galadriel and Celeborn, bore him two sons, Elladan and Elrohir, and a daughter, Arwen, at the dawn of the Third Age. She was captured by Orcs of the Misty Mountains in 2509 and rescued by her sons, but soon wearied of Middle-earth and departed over-sea.

During the Third Age, particularly after the fall of Arthedain in the war with Angmar, Elrond sheltered the chieftains of the Dúnedain and the line of Isildur in Rivendell. It was thus that Aragorn Elf-stone was brought up at Rivendell with the secret name Estel (‘Hope’) and Elrond was as a father to him.

Late in the Third Age Gandalf, Bilbo and the Dwarves found comfortable refuge there on their journey to Erebor, as described in The Hobbit. Bilbo later returned there on his way home, and when he left The Shire he wandered to Rivendell, and aside from a visit to Dale with the dwarves, remained there until leaving Middle-earth at the end of the Third Age. Frodo came to Rivendell with Aragorn, flying from the Nazgûl, and was healed by Elrond. The Fellowship of the Ring was formed there and the shards of Narsil, Elendil’s sword, re-forged and named Andúril by Aragorn. The Hobbits of the Fellowship returned there with many fair Elves after Aragorn’s wedding.

At the end of the Third Age Elrond set forth from Rivendell with Bilbo, Galadriel and many other high-Elven lords and ladies for the Grey Havens. Frodo and Gandalf departed with him over-sea, ending the Third Age.

‘What about Rivendell and the Elves? Is Rivendell safe?’ ‘Yes, at present, until all else is conquered. The Elves may fear the Dark Lord, and they may fly before him, but never again will they listen to him or serve him. And here in Rivendell there live still some of his chief foes: the Elven-wise, lords of the Eldar from beyond the furthest seas. They do not fear the Ringwraiths, for those who have dwelt in the Blessed Realm live at once in both worlds, and against both the Seen and the Unseen they have great power.’ ‘I thought that I saw a white figure that shone and did not grow dim like the others. Was that Glorfindel then?’ ‘Yes, you saw him for a moment as he is upon the other side: one of the mighty of the First-born. He is an Elf-lord of a house of princes.’

- Fellowship of the Ring

Then Elrond and Galadriel rode on; for the Third Age was over, and the Days of the Rings were passed, and an end was come of the story and song of those times. With them went many Elves of the High Kindred who would no longer stay in Middle-earth; and among them, filled with a sadness that was yet blessed and without bitterness, rode Sam, and Frodo, and Bilbo, and the Elves delighted to honour them.
...And when they had passed from the Shire, going about the south skirts of the White Downs, they came to the Far Downs, and to the Towers, and looked on the distant Sea; and so they rode down at last to Mithlond, to the Grey Havens in the long firth of Lune.

- Return of the King