Rivendell was built and settled by the ancient elves. Elrond himself lives there, he is the eldest of the elves of middle earth. Rivendell is also known as Imladris. It was established by the elves in the second age. It was built more than four thousand years ago before the events of Lord of the Rings.
The Council of Elrond
The Council of Elrond is where the most important discussions are held.