William returned to Normandy, summoned his lieges, and took the field promptly.  King Henry joined him at Argence, with a body of three thousand men-at-arms, and a battle took place on the 10th of August, 1047, at Val des Dunes, three leagues from Caen.  It was very hotly contested.  King Henry, unhorsed by a lance-thrust, ran a risk of his life; but he remounted and valiantly returned to the melley.  William dashed in wherever the fight was thickest, showing himself everywhere as able in command as ready to expose himself.  A Norman lord, Raoul de Tesson, held aloof with a troop of one hundred and forty knights.  “Who is he that bides yonder motionless?” asked the French king of the young duke.  “It is the banner of Raoul de Tesson,” answered William; “I wot not that he hath aught against me.”  But, though he had no personal grievance, Raoul de Tesson had joined the insurgents, and sworn that he would be the first to strike the duke in the conflict.  Thinking better of it, and perceiving William from afar, he pricked towards him, and taking off his glove struck him gently on the shoulder, saying, “I swore to strike you, and so I am quit:  but fear nothing more from me.”  “Thanks, Raoul,” said William; “be well disposed, I pray you.”  Raoul waited until the two armies were at grips, and when he saw which way victory was inclined, he hasted to contribute thereto.  It was decisive:  and William the Bastard returned to Val des Dunes really duke of Normandy.

He made vigorous but not cruel use of his victory.  He demolished his enemies’ strong castles, magazines as they were for pillage no less than bulwarks of feudal independence; but there is nothing to show that he indulged in violence towards persons.  He was even generous to the chief concocter of the plot, Guy of Burgundy.  He took from him the countships of Vernon and Brionne, but permitted him still to live at his court, a place which the Burgundian found himself too ill at ease to remain in, so he returned to Burgundy, to conspire against his own eldest brother.  William was stern without hatred and merciful without kindliness, only thinking which of the two might promote or retard his success, gentleness or severity.

There soon came an opportunity for him to return to the king of France the kindness he had received.  Geoffrey Martel, duke of Anjou, being ambitious and turbulent beyond the measure of his power, got embroiled with the king his suzerain, and war broke out between them.  The duke of Normandy went to the aid of King Henry and made his success certain, which cost the duke the fierce hostility of the count of Anjou and a four years’ war with that inconvenient neighbor; a war full of dangerous incidents, wherein William enhanced his character, already great, for personal valor.  In an ambuscade laid for him by Geoffrey Martel he lost some of his best knights, “whereat he was so wroth,” says a chronicle, “that he galloped down with such force upon Geoffrey, and struck him in such wise with his sword that he dinted his helm, cut through his hood, lopped off his car, and with the same blow felled him to earth.  But the count was lifted up and remounted, and so fled away.”