Historia Brittonum
The "Historia Brittonum", a 9th-century Latin historical compilation attributed in some late manuscripts to a Welsh cleric called Nennius, contains the first datable mention of King Arthur, listing twelve battles that Arthur fought. These culminate in the Battle of Badon, where he is said to have single-handedly killed 960 men. Recent studies, however, question the reliability of the "Historia Brittonum".