Rivendell is home to many elves, including Elrond and his daughter Arwen. Since it is inhabited by elves, Rivendell has a timeless quality to it for many Lord of the Rings fans. It seems that it must have always existed in Middle-earth and always would. However, some fans might wonder when Rivendell was established and what led to its establishment. In order to understand the answers to these questions, it is crucial to know the history of Middle Earth, and how Elrond and Sauron appear in that history.
Elrond is, as many Lord of the Rings fans probably know, rather old even for an elf. He was born in the First Age of Middle Earth to his parents Eärendil and Elwing. Elrond also had a twin brother Elros. Both brothers were offered a choice: they could live as men or Elves. Elrond, of course, chose to live the life of the Elves. Yet Elros made a different choice. He chose to become one of the race of Men and became the first King of Númenor.
Since Elrond chose to be an Elf, he became captain and herald of Elven King Gil-galad, the High King of the Ñoldor. It is Gil-galad who sends Elrond to Eregion in the Second Age 1695 to protect it from Sauron's forces. Unfortunately, Elrond and the other Elves arrive too late. They are also not a large enough army to truly protect the area from Sauron's armies. Because of this, Elrond retreats north with refugees from Eregion, including Celeborn, who is married, when Lord of the Rings fans meet him, to Galadriel.
Elrond, Celeborn, and the rest of the Elves only manage to escape from Sauron's armies because of Durin III's forces attacking Sauron's in the rear. It is then, over the next two years, that Elrond establishes Rivendell near the Misty Mountains. Rivendell becomes a sanctuary and stronghold for Elrond and the other Elves. And indeed for anyone not on Sauron's side in Middle Earth. For four years, Sauron's forces attack Rivendell.
Luckily, the Númenóreans arrive and help Elrond defeat Sauron's forces, at least temporarily. Gil-galad, the Elven King also helps out. Between Elrond's army, Gil-galad's, and the Númenórean forces, Rivendell is saved. It is then that Elrond hosts the first White Council in Rivendell. There it is decided that Rivendell will remain the final stronghold west of the Misty Mountains and that the Three Elven Rings will remain hidden. It is possible that Gil-galad, after the White Council, gave Elrond Vilya, one of the Three Elven Rings. It is also possible that Gil-galad kept both Vilya and Narya until the end of the Second Age.
Another important thing happens at this White Council meeting. This meeting is attended by Galadriel, and it is there that Elrond first meets her daughter Celebrían, who would later become his wife. Rivendell is truly important long before the War of the Ring. During the War of the Last Alliance of Elves and Men, the Elves go from Rivendell to Mordor. This war, as Lord of the Rings fans know, ends with Sauron temporarily defeated and the Ring out of his possession. Isildur takes the One Ring from Sauron, though Elrond does try to convince him to throw it into Mount Doom.
Unfortunately, Isildur refuses and Elrond goes back to Rivendell after the war is over. During the Third Age, in 109, Elrond and Celebrían get married. In the Lord of the Rings books, they have three children: twin boys Elladan and Elrohir and later on, Arwen. In the Lord of the Rings movies, however, Elladan and Elrohir are not truly mentioned. Rivendell is also important in that it is where Aragorn grew up. Elrond took him in after his father's demise, naming him Estel, which means hope in Sindarin. Aragorn grew up unaware of his destiny and his royal blood until he reached adulthood when Elrond told him.
Rivendell is also a sanctuary for all those who oppose Sauron. Indeed, Bilbo, Thorin Oakenshield, and the rest of their company stay there for a while on their way to retake the Lonely Mountain from the dragon Smaug. While they're there Elrond helps them translate the Moon Writing on Thorin's map. Of course, Rivendell is also important during the events of Lord of the Rings. It is at the Council of Elrond in Rivendell that the Fellowship of the Ring is formed, and it is there Frodo volunteers to bring the One Ring to Mount Doom.
Elrond lives in Rivendell until the One Ring and Sauron are both destroyed. Then he goes to Minas Tirith for two reasons, at least in the Lord of the Rings books, to give the Sceptre of Annúminas to Aragorn, who is now King. And to give his daughter Arwen away in marriage to Aragorn. The latter also happens in the Lord of the Rings movies. On September 29, 3021, Elrond leaves Middle Earth for the Undying Lands with the other bearers of the Elven Rings. Rivendell is then left empty. But it at least was a true sanctuary and stronghold for those who opposed Sauron, for as long as it lasted.