While the Bretons were fighting against Richard I., Constance, the mother of Arthur, relinquished their support, and carried her son first to the court of Richard, and then to that of the King of France. When John ascended the throne, Arthur was placed under the protection of Philip, to whom the boy-prince was made to surrender the independence of Brittany, Maine, Touraine, and Anjou, by acknowledging him as feudal suzerain of those provinces. Constance was a woman of little virtue, and seems to have cared more about the prosecution of her own intrigues than the welfare and safety of her child. The Bretons, headed by William Desroches, firmly maintained the attitude they had assumed; while John, with his army of mercenaries, advanced upon their lands, spreading ruin and devastation around him--burning the villages, and selling the inhabitants as slaves. Philip marched a body of troops to the assistance of Desroches, took possession of several towns of Brittany, and seized some castles on the frontiers belonging to the English. He, by way of securing Arthur for the future, conferred upon him the honour of knighthood, and even promised him the hand of his daughter Mary in marriage. This friendly attitude, however, did not exist long. Philip soon perceived that it was impossible to retain possession of his new territories, so long as he was opposed by the inhabitants themselves on the one hand, and the arms of the King of England on the other. He therefore determined to arrange a peace with John, and for that purpose he completely sacrificed the interests of the young prince, to whom he had so lately promised an alliance with himself. By a treaty concluded in the following year (1200) between the two kings, it was agreed that John should retain possession of all the provinces held by his father, and Arthur was compelled to do homage to his uncle for Anjou, Brittany, and Maine. In return John did homage to Philip for his French possessions. The treaty was cemented by a marriage alliance; John promising to young Louis, the French king's heir, the hand of his niece, Blanche of Castille.