A purely hypothetical ‘very ancient book in the British language’ (quendam Brittanici sermonis librum uetustissimum) containing a history of the deeds of the kings of Britain, from Brutus to Cadwalladr, which Geoffrey of Monmouth alleges to have rendered into Latin when writing his Historia regum Britanniae, a work known for its audacious originality. Geoffrey mentions it in the preface to this work, where he claims to have received the book from Walter, archdeacon of Oxford. Whatever his source material may have been, or Walter’s role in supplying it, the claim that so much of this was written in the vernacular and contained in a single volume (implicitly, to which few would have access) is commonly regarded as a spurious appeal to authority.
