From The Art and Popular Culture Encyclopedia
"In the time of this good king that famous order of chivalry of the Knights of the Round Table was instituted, and the amour of Don Lancelot of the Lake with the Queen Guinevere occurred, precisely as is there related, the go-between and confidante therein being the highly honourable dame Quintañona."--Don Quixote (1605) by Miguel de Cervantes
King Arthur was a legendary British leader who, according to medieval histories and romances, led the defence of Britain against Saxon invaders in the late 5th and early 6th centuries. The details of Arthur's story are mainly composed of Welsh and English folklore and literary invention, and modern historians generally agree that he is unhistorical. The sparse historical background of Arthur is gleaned from various sources, including the Annales Cambriae, the Historia Brittonum, and the writings of Gildas. Arthur's name also occurs in early poetic sources such as Y Gododdin.
Arthur is a central figure in the legends making up the Matter of Britain. 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 (History of the Kings of Britain). How much of Geoffrey's Historia (completed in 1138) was adapted from such earlier sources, rather than invented by Geoffrey himself, is unknown.