While Bilbo Baggins dwelt in Rivendell, he made use of all the resources there (including the memories of living Elves) to write four scholarly volumes bound in red leather. The first of these, the Red Book of Westmarch, was continued by Bilbo's heir, Frodo. It was copied many times, and became the original source for our modern The Hobbit and The Lord of the Rings.

The Hobbits of the Shire, though, seem to have had less interest in the other three volumes, originally entitled simply Translations from the Elvish, that told the tales of the ancient First Age going back to the making of the world. Only one copy was made, in Gondor in IV 172, and this was kept at Great Smials by the Took family, and it thus became known as the Thain's Book. It is from this copy that The Silmarillion in its modern form derives.¹

The Silmarillion, which in its own words passes 'from the high and the beautiful to darkness and ruin'² actually consists of a corpus of five works, of which the Quenta Silmarillion is the central tale. These are:

• Ainulindalë, the tale of the Music of the Ainur and the creation of Arda.
• Valaquenta, the tale of the Valar, in which the nature of each of the Powers is described.
• Quenta Silmarillion, the longest tale, which gives an account of the history of Arda from its beginnings until the end of the First Age.
• Akallabêth, the tale of the Second Age, which concentrates on the history of Númenor until its Downfall.
• Of the Rings of Power and the Third Age, which spans the late Second Age and the Third, telling of the forging of the Rings of Power and their history up to the War of the Ring.

The documents that lay behind these works came from various sources. Ainulindalë, for example, was a very ancient work attributed to Rúmil the sage of Tirion. The Quenta Silmarillion itself seems to have been developed in Númenor during the Second Age, though parts of it (particularly the Narn i Chîn Húrin) were said to date back to the First Age.

The final section, Of the Rings of Power and the Third Age must have different origins than the rest of the work. It cannot have been written or translated by Bilbo, since it contains an account of his own departure from Middle-earth. Its source is never stated directly, but a short reference about Peregrin Took in the Prologue to The Lord of the Rings provides a hint: '...he and his successors collected many manuscripts written by scribes of Gondor: mainly copies or summaries of histories or legends relating to Elendil and his heirs.' This was the likely route by which Of the Rings of Power (and probably also Akallabêth) came to be included in the Thain's Book.