Nennius was a student of Elvodugus, commonly identified with the bishop Elfodd of Bangor[3] who convinced British ecclesiastics to accept the Continental dating for Easter, and who died in 809 according to the Annales Cambriae.
[7] The Historia Brittonum was highly influential, becoming a major contributor to the Arthurian legend, in particular for its inclusion of events relevant to debate about the historicity of King Arthur.
[13] Originally written as a history of the Britons in an attempt to document a legitimate past, the Historia Brittonum contains stories of legend and superstition alike.
[15] Nennius makes several attempts to trace the history of the Britons back to the Romans and Celts through his empirical observations of what he refers to as "The Marvels" or "Wonders of Britain".
It appears in the first instance as a marginal gloss contained in a MS. of the twelfth century;' under ordinary conditions, the chapter would unhesitatingly be set aside as a forgery.
David N. Dumville argues that the manuscript tradition and nature of the Prologue in particular fail to substantiate the claim that Nennius was the author of Historia Brittonum.
In his argument against Zimmer, he cites a textual inconsistency in the Irish translation regarding a place called Beulan, concluding that "we must admit to ignorance of the name of [the Historia's] ninth-century author.