The Book of Lost Tales stands at the beginning of the entire conception of Middle-earth and Valinor, for the Tales were the first form of the myths and legends that came to be called The Silmarillion.
Embedded in English legend and English association, they are set in the narrative frame of a great westward voyage over the Ocean by a mariner named Eriol (or Elfwine) to Tol Eressea, the Lonely Isle, where Elves dwelt; from them he learned their true history, the Lost Tales of Elfinesse. In the Tales are found the earliest accounts and original ideas of Gods and Elves, Dwarves, Balrogs, and Orcs; of the Silmarils and the Two Trees of Valinor; of Nargothrond and Gondolin; of the geography and cosmology of the invented world.