The two armies entered Normandy; that which was to act on the left of the Seine was led by the King, the other by his brother Odo.  Against the King William made ready to act himself; eastern Normandy was left to its own loyal nobles.  But all Normandy was now loyal; the men of the Saxon and Danish lands were as ready to fight for their duke against the King as they had been to fight against King and Duke together.  But William avoided pitched battles; indeed pitched battles are rare in the continental warfare of the time.  War consists largely in surprises, and still more in the attack and defence of fortified places.  The plan of William’s present campaign was wholly defensive; provisions and cattle were to be carried out of the French line of march; the Duke on his side, the other Norman leaders on the other side, were to watch the enemy and attack them at any favourable moment.  The commanders east of the Seine, Count Robert of Eu, Hugh of Gournay, William Crispin, and Walter Giffard, found their opportunity when the French had entered the unfortified town of Mortemer and had given themselves up to revelry.  Fire and sword did the work.  The whole French army was slain, scattered, or taken prisoners.  Ode escaped; Guy of Ponthieu was taken.  The Duke’s success was still easier.  The tale runs that the news from Mortemer, suddenly announced to the King’s army in the dead of the night, struck them with panic, and led to a hasty retreat out of the land.

This campaign is truly Norman; it is wholly unlike the simple warfare of England.  A traitorous Englishman did nothing or helped the enemy; a patriotic Englishman gave battle to the enemy the first time he had a chance.  But no English commander of the eleventh century was likely to lay so subtle a plan as this, and, if he had laid such a plan, he would hardly have found an English army able to carry it out.  Harold, who refused to lay waste a rood of English ground, would hardly have looked quietly on while many roods of English ground were wasted by the enemy.  With all the valour of the Normans, what before all things distinguished them from other nations was their craft.  William could indeed fight a pitched battle when a pitched battle served his purpose; but he could control himself, he could control his followers, even to the point of enduring to look quietly on the havoc of their own land till the right moment.  He who could do this was indeed practising for his calling as Conqueror.  And if the details of the story, details specially characteristic, are to be believed, William showed something also of that grim pleasantry which was another marked feature in the Norman character.  The startling message which struck the French army with panic was deliberately sent with that end.  The messenger sent climbs a tree or a rock, and, with a voice as from another world, bids the French awake; they are sleeping too long; let them go and bury their friends who are lying dead at Mortemer.  These touches bring home to us the character of the man and the people with whom our forefathers had presently to deal.  William was the greatest of his race, but he was essentially of his race; he was Norman to the backbone.