King Arthur is a legendary British leader who, according to Medieval histories and romances, led the defence of Britain against Saxon invaders in the early sixth century. The details of Arthur's story are mainly composed of folklore and literary invention, and his historical existence is debated and disputed by modern historians. The legendary Arthur developed as a figure of international interest largely through the popularity of Geoffrey of Monmouth's fanciful and imaginative 12th-century Historia Regum Britanniae. Some Welsh and Breton tales and poems relating the story of Arthur date from earlier than this work; in these works, Arthur appears either as a great warrior defending Britain from human and supernatural enemies or as a magical figure of folklore, sometimes associated with the Welsh Otherworld, Annwn.