Geoffrey of Monmouth introduces Guinevere, "the loveliest woman in all the island" with her marriage to Arthur. He proudly states that she "descended from a noble family of Romans and reared in the household of Duke Cador" implying a fair match. Monmouth's interests lie primarily in the legitimizing effect of Guinevere's Roman blood.
Yet her ancestry earns no forgiveness when Guinevere breaks "the oath of her prior nuptials" by becoming queen to the usurping Modred. Earlier accounts, in accordance with the attitudes of the early Latin texts discussed above, assumed that
Guinevere accompanied the throne as Queen, as spoils to the victor. Monmouth, however, attributes her newfound allegiance not to her situation but to "unconscionable lust" (91). Rather than see Guinevere as a "mere pawn of political events," Monmouth paints her as Modred's accomplice.
Even before Chreitien introduced Lancelot, Guinevere's reputation caught up with her. Just as she
finally became a noteworthy character, Guinevere shouldered some of the blame for the fall of Camelot through her betrayal of Arthur, continuing the Welsh tradition of her traitorous nature.
Women's History Magazine