The History of the Britons (Latin: Historia Brittonum) is a purported history of early Britain written around 828 that survives in numerous recensions from after the 11th century. The Historia Brittonum is commonly attributed to Nennius, as some recensions have a preface written in that name. Some experts have dismissed the Nennian preface as a late forgery and argued that the work was actually an anonymous compilation. Publication History. Manuscripts. At least 5 manuscripts preserve the Historia, with the Harleian being the most complete.
https://en.wikipedia.org/wiki/Historia_Brittonum