487] All the hereditary provinces of William, as well as his family, were during several years thrown into convulsions by this war; and he was at last obliged to have recourse to England, where that species of military government, which he had established, gave him greater authority than the ancient feudal institutions permitted him to exercise in Normandy.
He called over an army of English under his ancient captains, who soon expelled Robert and his adherents from their retreats, and restored the authority of the sovereign in all his dominions.

The young prince was obliged to take shelter in the castle of Gerberoy, in the Beauvoisis, which the king of France, who secretly fermented all these dissensions, had provided for him.

In this fortress he was closely besieged by his father, against whom having a strong garrison, he made an obstinate defence.

There passed under the walls of this place many rencounters which resembled more the single combats of chivalry than the military actions of armies; but one of them was remarkable for its circumstances and its event.

Robert happened to engage the king, who was concealed by his helmet, and, both of them being valiant, a fierce combat ensued, till at last the young prince wounded his father in the arm and unhorsed him.