Historia Brittonum
Nennius was traditionally credited with having written the "Historia Brittonum" c. 830. 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. It also includes the legendary origins of the Picts, Scots, St. Germanus and Vortigern, and documents events associated with the Anglo-Saxon invasion of the 7th century as contributed by a Northumbrian document.