The Silmarillion

The Silmarilli were three perfect jewels created by Feanor, most gifted of the High Elves. When the first Dark Lord, Morgoth, stole the jewels and set them within an iron crown in the impenetrable fortress of Angband, Feanor and his kindred took up arms against the gods and waged a long and terrible war to recover them.

J. R. R. Tolkien