It is generally agreed that Arthurian literature, as a written phenomenon with more or less datable texts, begins with Geoffrey of Monmouth and stems from his Historia regum Britanniae. At its inception, then, it is a genre associated not with storytelling but with what purports to be the faithful recording of real events preserved in reliable sources by writers who can be considered as trustworthy, as authorities. Although Geoffrey mentions oral tradition in his Dedication, the main prop of his own enterprise and of his own claim to respectability is an alleged written source provided by an unimpeachable agent, Archdeacon Walter of Oxford, who is credited with furnishing him "a very old book in British."1 Furthermore, the earlyBritish material in Geoffrey's own book is anchored in time through plentiful references to events in the Old Testament and also to such solidly historical personages as Julius Caesar and Constantine the Great. Such matters reassuringly serve as prelude to the conception, birth, career, conquests, and disappearance of Arthur and the passage of dominion2 to later British rulers. If much of this is spurious, some of it looked sufficiently historical for Geoffrey's contemporaries, and successive generations of medieval readers (aside from a few tough-minded skeptics), to take it as historical. They mentally classified it in a familiar genre, that of historiography.