It is perhaps the story of Lanval that has the clearest message of any of Marie de France's lais regarding her reversal of cultural gender roles. Rather than the men being dominant and holding societal power, which was certainly the norm during the Middle Ages, Marie chooses to make the women the controlling and shaping forces in this story.
There are two central female characters in this story. The first is the mysterious lady with whom the knight Lanval falls in love. She is consistently described throughout the story as the most powerful character. Firstly, Marie explains that she is impossibly wealthy. The lady's wealth is the first thing that Lanval himself notices when her two serving women usher him to her tent.
They led him to the tent, which was beautiful and luxurious. Neither Queen Semiramis, however much wealth, power, and knowledge she had, nor Emperor Octavian could have afforded even the flap of the tent. On top of it was a golden eagle; I cannot even guess the value of it, or of the ropes and poles that supported the walls. No king on earth, no matter how extravagant he might be, could have afforded it.
The lady is described as more beautiful than any other, giving her yet another dimension of power. Once Lanval sees her, he instantly falls in love with her, and the two spend the afternoon together. Then, the lady is the one, not Lanval, who sets the standards for their relationship going forward. She tells him,
I warn you and command and entreat you never to reveal this to anyone. And I will tell you the truth. If our love were ever revealed, you would lose me forever. Never again could you see me.
Once Lanval does reveal her existence, she demonstrates her power over him by refusing to come when he calls as she promised. However, ultimately, she does choose to come to him. Her method of saving Lanval as the "knight in distress" solidifies her position in the story. She sends multiple envoys before her own arrival to Arthur's court so that he can prepare for her coming. Her assumption that Arthur's home would not be suitable enough for her again points back to her massive wealth and position. When she does arrive, rather than staying to enjoy the attempts at making everything worthy of her, she leaves as the conquering maiden with her dear knight holding onto her.
He was freed by their decision, and the maiden, with her many servants, left. The king could not keep her there. Outside the room there was a large stone of dark marble, where the heavily armed men mounted their horses when they left the king’s court. Lanval stood on it, and when the maiden came riding through the door, Lanval leapt on the palfrey behind her.
The other woman portrayed as extremely powerful is Arthur's wife, Guinevere. Despite the cultural norm that men were supposed to compliment and flirt with the women and women were supposed to reject them and remain cold, Guinevere approaches Lanval and boldly offers herself to him, demonstrating a strong sense of sexuality and confidence. When he rejects her, she continues to use her social power and influence over her husband by demanding that Lanval pay for his affront on her honor. She claims "that Lanval had shamed her by asking for her love; when she refused, he insulted her." Then, once he is accused and brought before the court, Guinevere continues to use her influence over her husband to move things along. Marie describes, "The king pressed them because the queen was waiting for them," and it is only the appearance of Lanval's mysterious lady that saves him.
These two women, though certainly different in character and role, demonstrate the massive societal power that is shifted from men to women in this lai.