The Morte D'Arthur was completed in 1469/70 by Thomas Malory. William Caxton's edition of 1485 was the only edition until 1934. Caxton altered the manuscripts extensively.

The original manuscripts show the following composed Mallory's Works.
1St: Founding of Arthur's Kingdom and the Round Table
2nd: Arthur's campaign for Rome
3rd: Adventures of Lancelot
4th: Romance of Gareth
5th: Romance of Tristan
6th: Quest for the Holy Grail
7th: Lancelot's return to court and romance with Guinevere
8th: Breakup of the Table and the end of all Arthur's Knights.

The story is not told in chronological order but is a series of narratives. Its largest source is the massive cycle of Arthurian narrative compiled in 13th C France. Malory's narrative is structured as an investigation into the meaning of the codes and ethos of that world. The institution of the Round Table is meant to introduce a civilizing code of behavior to Arthur's kingdom, but the knights' adventures show the difficulty of working out a chivalric ethos in practice.
     The narrative explores and celebrates chivalric values but doesn't get narrowly moralistic nor give a simple explanation of why Arthur's brave new world collapses in disarray. No single chain of actions causes the breakdown of the Round Table. The relationships between actions and events is more mysterious than in the Old French sources.

The ultimate source for the legend, the one going back furthest, is Geoffrey of Monmouth's Historia Regum Britanniae. Geoffrey was a 12th Century Welsh monk who created a history of England from the oral traditions of his time, although he cites as a source an ancient manuscript in Welsh that contains the lives and deeds of all their kings from Brutus to the coming of Julius Caesar. Geoffrey's history covers to the death of Cadwalader in 689. Geoffrey mixes pagan and Christian legends, chronicles, and comment, with "pure invention." Arthur first appears in Geoffrey of Monmouth's History of the Kings of Britain in 1136. He is at the height of success, has defeated the Roman army, and is ready to go into Italy, when he gets news of Mordred's perfidy. He then returns to fight Mordred. Geoffrey's story is in prose Latin and, like ancient hero stories (eg Beowulf), lacks romantic elements.

In the French, Le Roman de Lancelot du Lac (1225-1230) speaks of Lancelot, the quest for the Grail, and the death of Arthur. Lancelot fails to achieve the Grail which is the measure of earthly chivalry. He also fails to save Arthur and the kingdom which suggests a gap in the earthly and spiritual parts of Arthur's kingdom.

The earliest English versions of the legend are Layamon's Roman de Brut (1190's) and the alliterative Morte Arthure (1360). Both have Arthur at the center and the story is a disaster because of disloyalty.
The Alliterative Morte Arthure was the source for Malory's book 2. This recounted the events from Arthur's campaign in Rome to his final battle against Mordred, concluding with his death. It follows the basic frame provided by Geoffrey of Monmouth, but it elaborates and adds, before the final battle, a remarkable dream sequence that features the vision of the Nine Worthies organized on Fortune's Wheel

The Nine Worthies:

          Pagan = Hector, Alexander, Julius Caesar
          OT = Joshua, David, Judas Maccabeus
          Christian = Arthur, Charlemagne, Godfrey of Bouillon

The dream is a transhistorical meditation on the nature of forces shaping Arthur's history.

Another source for Malory was the Stanzaic Morte Arthure used in the final books. It dates from the mid- to late-fourteenth century.  Mallory ignores the link between Lancelot and the Grail themes. Thus late Arthurian narrative portrays the love affair between Lancelot and Guinevere, the enmity between Gawain and Lancelot, and the treachery of Mordred as all leading to Arthur's destruction.
      Lancelot is not part of Geoffrey's History. His story may have come from an Anglo-Norman narrative, but the earliest extant version is a story by Chretien de Troyes, 13th century France. Galahad is his son through a brief liaison with Elaine, daughter of King Pellas.

      Mordred is mentioned in 10th C Welsh annals. Geoffrey of Monmouth says that Arthur's nephew (Mordred) usurps his throne and takes Guinevere for his love while Arthur is in Rome. In narratives after Geoffrey, Mordred is seen as Arthur's illegitimate son conceived through a brief relation with his half-sister Morgause. Morgause (post-Geoffrey) is the wife of King Lot and the mother of Gawain, Gaheris, Agraivain, and Gareth. She is killed by Gaheris when she is discovered in adultery.

Morgan La Fay: In Geoffrey's life of Merlin, she is the Lady of the Lake. She has magic powers and is in charge of nine women of Avalon who receive Arthur after his final wound. In later versions, including Malory's, her role is more ambiguous. She both assists and obstructs the foundation of Arthurian society. She is identified with Arthur's half-sister, is the wife of Luca, and daughter of Igraine. She uses her magic powers to ensnare men, but she is still one of the women who escort Arthur to Avalon. Recently she is seen as more complex--she is a focus of feminine power and independence especially in Marian Zimmer Bradley's Mists of Avalon.