>>24818226 (OP)
Historia Brittonum. Online sources are conflicted when Nennius lived while an opening preface refers to the year 858 in the reign of Merfyn Frych, who apparently died in 844 according to the Annales Cambriae. Meanwhile, there's every clue that he actually lived two centuries earlier in the 7th. A letter referring to a fire and a man named Nennius listed among the survivors, a first edition book reportedly written in the 630s, and the last writer he lists as inspiration is Isidore- probably of Seville who lived around that time.
As for his history, it is refreshing after leafing through the lamentations and British hatred held by Gildas and the two-faced approach of Bede, who runs cover for his little rats just because they're in the same church as him, and refusing to write history about major figures because they were pagan (his own words).
Nennius is more organized and actually covers the ancient stuff too. Next I'll finish a full reading of Annales Cambriae, then a few works of churchmen who reference mythological heroes of Britain, and after that the History of the Kings of Britain.