On the 20th and 21st of September 1792 the Convention met, the Bourbon monarchy fell, and the Duke of Brunswick was defeated, a coincidence of memorable events. Brunswick, pushing on from Verdun into the defiles of the Argonne, had two armies operating against him, trying to stop his march; the one under Dumouriez, the other under Kellermann. He forced a way, however, but at the further side, about the hills of Valmy, had to face the combined armies of his adversaries. Brunswick was now much reduced by sickness, and was much worried over supplies and his lengthening line of communications. In a faint-hearted way he deployed for attack. Dumouriez for the moment checked him by a skillful disposition of his superior artillery. But if the superbly drilled Prussian infantry were sent forward it seemed as though the result could not be long in doubt. {158} Brunswick methodically and slowly made his preparations for the attack, but just at the moment when it should have been delivered, Dumouriez, divining his opponent's hesitation, imposed on him. Riding along the French front with his staff he placed his hat on the point of his sword and rode forward, singing the Marseillaise. His whole army catching the refrain advanced towards the enemy; and Brunswick at once took up a defensive attitude, which he maintained till the close of the battle. The unsteady battalions and half-drilled volunteers of Dumouriez had suddenly revealed the fact that they were a national army, and that they possessed the most formidable of military weapons, patriotism. That was an innovation in 18th-century warfare, an innovation that was to result in some notable triumphs. At Valmy it led to the Prussians retiring from a battle field on which they had left only a few score of dead. Soon afterwards Brunswick began a retreat that was to lead him back to the Rhine.