‘Translations from the Elvish’

Three red-bound volumes of lore assembled by Bilbo Baggins during his time in Rivendell before the War of the Ring, between the years III 3003 and III 3018. Drawing on the resources of Rivendell (not only its library, but also living Elves who had experienced the events themselves) the Translations contained an account of the history of the Elder Days. They became part of the Red Book of Westmarch, and were included in the copy known as the Thain's Book, and thus were preserved for posterity through the copy of that book made by Findegil in Gondor.

It is implied that Bilbo's work was the fictional source material for The Silmarillion, just as his diary (with Frodo's additions) formed the basis of The Hobbit and The Lord of the Rings. This is nowhere stated categorically, but the fact that these three volumes described the same historical period as The Silmarillion, and were expressly preserved for later ages, strongly suggests that this was Tolkien's intention.