The first definite mention of Arthur appears in 829, where he is presented as a military leader fighting against the invading Saxons in 5th- to 6th-century Sub-Roman Britain at the Battle of Badon, written more than three centuries after the events depicted. He develops into a legendary figure in the Matter of Britain from the 12th century, following Geoffrey of Monmouth's influential but largely fictional "Historia Regum Britanniae".