The Best Knight Barred From His Own Quest

By the time the Arthurian legend absorbs the Grail material, above all in the Vulgate Cycle's Queste del Saint Graal, Lancelot's very greatness as a knight becomes the measure of what his affair with Guinevere costs him. He rides in the Grail quest as the acknowledged best fighter of the Round Table, yet is granted only a partial, distant vision of the Grail rather than the full achievement reserved for a knight of unstained purity, his sin with the queen standing between him and the object his own son will attain in his place. That son, Galahad, is conceived under deliberate deception: Elaine of Corbenic, daughter of the Grail's guardian king, uses enchantment to make Lancelot believe he lies with Guinevere when he in fact lies with her, a trick specifically engineered because prophecy holds that only Lancelot's bloodline can produce the knight destined to achieve the Grail, and only through such deceit could that bloodline exist at all given Lancelot's fixed devotion to the queen. Galahad succeeds where his father cannot, achieving the Grail fully and dying soon after in a state of grace, while Lancelot returns to the ordinary, compromised world of Camelot and to the affair that will, within the same cycle's larger story, help bring the whole fellowship down. The Grail material does not punish Lancelot by stripping his prowess; it simply draws a line his prowess alone cannot cross, and lets that line define him as clearly as any victory in single combat does.