In the summer of 1047, Duke William II (”The Conqueror”) was still in the youth of his reign as lord over Normandy. He had succeeded to the position of duke in 1035 after the death of his father, Duke Robert I. This period in Normandy’s history was an unstable time, with rebellion always a possibility by rivals of William who felt they had equal rights to the title of the duchy. While Robert, Archbishop of Rouen, was alive, the duchy remained in relative peace, but after his death, the rebels began to push more toward all out rebellion.
One of the persons who believed he had a more legitimate claim to the title of Duke was William’s cousin, Gui of Burgundy. In 1046, Gui along with other rebel nobles (Nigel of the Contentin, Rannulf of the Bessin, Ralph Tesson of Thury, Haimo of Creully) set an ambush for William near Valognes. William managed to escape, and he sought the protection of his overlord, King Henry I of France.
In effect, Normandy was under the king’s rule, and William was his vassal, and since the rebels had threatened a vassal of the king, they had indirectly threatened the king himself. And so in 1047, King Henry gathered his forces, joined with William’s army in Normandy near Caen, and marched south to the plain of Val-ès-Dunes, near the present day town of Conteville.
The battle consisted mostly of cavalry charging one another. The Normans had yet to employ fully the tactics William would later use at the Battle of Hastings: a mixture of archers, infantry, and horsemen. While the rebel armies supposedly outnumbered the other side, they did not have the same leadership, and King Henry and William drove their enemies into the Orne River. One contemporary account observed how the bodies floating in the river blocked the mill of Barbillon downstream.
With the duchy secure for the time being, the Church forced the rebel barons to declare a “Truce of God,” meaning they agreed not to wage private wars on certain days of the week (Wednesday evening to Monday morning) and during certain religious observances (e.g., - Easter, Lent, etc.). William and the king, however, were not forced to follow these same rules. Even with the “Truce of God,” the test of William’s resolve and strength as a leader was not ending. It was only the beginning for William, a young ambitious duke who would later rise to prominence as one of the most legendary figures in the pages of history.
Douglas, David C. William the Conqueror : The Norman Impact upon England. Berkeley, Calif. : University of California, 1964.