The battle of Mt. Badon—in which, according to the Annales Cambriae (c.1150), Arthur carried the Cross of Jesus on his shoulders—but not Arthur's name, is mentioned (c.540) by Gildas. The earliest apparent mention of Arthur in any known literature is a brief reference to a mighty warrior in the Welsh poem Gododdin (c.600). Arthur next appears in Nennius (c.800) as a Celtic warrior who fought (c.600) 12 victorious battles against the Saxon invaders.
These and several subsequent references indicate that his legend had already developed into a considerable literature before Geoffrey of Monmouth wrote his Historia (c.1135), in which he elaborated on the feats of King Arthur whom he represented as the conqueror of Western Europe. After Geoffrey's Historia came Wace's Roman de Brut (c.1155), which infused the legend with the spirit of chivalric romance. The Brut (c.1200) of Layamon, modeled on Wace's work, gives one of the best pictures of Arthur as a national hero.
Chrétien de Troyes, a 12th-century French poet, wrote five romances dealing with the knights of Arthur's court. His Perceval contains the earliest extant literary version of the quest of the Holy Grail (see Grail, Holy). Two medieval German poets important in the development of Arthurian legend are Wolfram von Eschenbach and Gottfried von Strassburg. The latter's Tristan was the first great literary treatment of the Tristram and Isolde story.
After 1225 no significant medieval Arthurian literature was produced on the Continent. In England, however, the legend continued to flourish. Sir Gawain and the Green Knight (c.1370), one of the best Middle English romances, embodies the ideal of chivalric knighthood. The last important medieval work dealing with the Arthurian legend is the Morte d'Arthur of Sir Thomas Malory, whose tales have become the source for most subsequent Arthurian material. Many writers have used Arthurian themes since Malory, notably Tennyson in his Idylls of the King. Swinburne, William Morris, and Edwin Arlington Robinson also wrote poetic works based on the legend. T. H. White's trilogy The Once and Future King (1958) is a charming and decidedly 20th-century retelling of the Arthurian story.
Formerly, it was thought that the Arthurian legend was the work of several inventive poets and romancers of the Middle Ages. The generally accepted theory now is that Arthurian legend developed out of stories of Celtic mythology. The most archaic form in which these occur in British sources is the Welsh Mabinogion, but much of Irish mythology is palpably identical with Arthurian romance.
It is probable that traditional Irish hero stories fused in Britain with those of the Welsh, the Cornish, and the Celts of North Britain. The resultant legend with its hero, Arthur, was transmitted to their Breton cousins on the Continent probably by the year 1000. The Bretons, famous as wandering minstrels, followed Norman armies over Western Europe and used the legend's stories for their repertory. By 1100, therefore, Arthurian stories were well known even in Italy.
Although there are innumerable variations of the Arthurian legend, the basic story has remained the same. Arthur was the illegitimate son of Uther Pendragon, king of Britain, and Igraine, the wife of Gorlois of Cornwall. After the death of Uther, Arthur, who had been reared in secrecy, won acknowledgment as king of Britain by successfully withdrawing a sword from a stone. Merlin, the court magician, then revealed the new king's parentage. Arthur, reigning in his court at Camelot, proved to be a noble king and a mighty warrior. He was the possessor of the miraculous sword Excalibur, given to him by the mysterious Lady of the Lake.
Of Arthur's several enemies, the most treacherous were his sister Morgan le Fay and his nephew Mordred. Morgan le Fay was usually represented as an evil sorceress, scheming to win Arthur's throne for herself and her lover. Mordred (or Modred) was variously Arthur's nephew or his son by his sister Morgawse. He seized Arthur's throne during the king's absence. Later he was slain in battle by Arthur, but not before he had fatally wounded the king. Arthur was borne away to the isle of Avalon, where it was expected that he would be healed of his wounds and that he would someday return to his people.
Two of the most invincible knights in Arthur's realm were Sir Tristram and Sir Launcelot of the Lake. Both of them, however, were involved in illicit and tragic love unions—Tristram with Isolde, the queen of Tristram's uncle, King Mark; Launcelot with Guinevere, the queen of his sovereign, King Arthur. Other knights of importance include the naive Sir Pelleas, who fell helplessly in love with the heartless Ettarre (or Ettard) and Sir Gawain, Arthur's nephew, who appeared variously as the ideal of knightly courtesy and as the bitter enemy of Launcelot.
Also significant are Sir Balin and Sir Balan, two devoted brothers who unwittingly slew one another; Sir Galahad, Launcelot's son, who was the hero of the quest for the Holy Grail; Sir Kay, Arthur's villainous foster brother; Sir Percivale (or Parsifal); Sir Gareth; Sir Geraint; Sir Bedivere; and other knights of the Round Table. To modern readers, Arthurian legend has become the mirror of the ideal of medieval knighthood and chivalry.
See studies by R. H. Fletcher (2d ed. 1966), R. L. Loomis (1949; 1956; 1927, repr. 1969; 1963, repr. 1970), L. Alcock (1972), J. Morris (1973), and R. W. Barber (1973); J. L. Weston, tr., Arthurian Romances Unrepresented in Malory's Morte d'Arthur (8 vol., 1907; repr. 1971); N. J. Lacy et al., ed., The Arthurian Encyclopedia (1987); E. Archibald and A. Putter, ed., The Cambridge Companion to the Arthurian Legends (2009).
Norma Lorre Goodirch suggests in her book, King Arthur, that Camelot simply means Castle of the Hammer, which she suggests Arthur was called, thus could be any castle which he temporarily made his base.
Glastonbury is conceived of as the legendary island of Avalon. An early Welsh story links Arthur to the Tor in an account of a conflict between Arthur and the Celtic king, Melwas, who was said to have kidnapped Arthur's wife Queen Guinevere. In 1191, monks at the Abbey claimed to have found the graves of Arthur and Guinevere to the south of the Lady Chapel of the Abbey church, which was visited by a number of contemporary historians including Giraldus Cambrensis. The remains were later moved, and lost during the Reformation. Many scholars suspect that this discovery was a pious forgery to substantiate the antiquity of Glastonbury's foundation, and increase its renown. Others have suggested that the monastery was desperately short of funds at the time, and staged the "discovery" as a means of increasing pilgrimage (and thus, offerings and alms from those coming to see the remains of the famous king). If the latter supposition is true, then the deception worked - after the discovery, the abbey became wealthy for some time to come.
An alternative explanation has been suggested, that Arthur was originally buried on Abbey property at Nyland Hill and the remains translated to the Abbey itself during the abbacy of Dunstan in the 900s.
A cross was extant in Wells, not far from Glastonbury, on which were inscribed the Latin words HIC IACET SEPVLTVS INCLITVS REX ARTVRVS IN INSVLA AVALONIA (trans. "Here lies interred the renowned King Arthur in the Isle of Avalon"). However, many modern scholars suggest that the cross was a forgery - the Latin used being of a dialect common to the period of discovery (and not to the period when Arthur would have been buried). The fate of the cross after the 18th century is unknown.
A possible location of Avalon consistent with the theory of a northern Arthur, is the Roman fort of Aballava. Aballava, also called Avallana, was at the western end of Hadrian's Wall near the modern settlement of Burgh-by-Sands, Cumbria.
Bardsey Island has also been identified as a possible Avalon.