Up to this date the policy of Philip had coincided with the interests of his great communes in Flanders and his popularity throughout the county was unbounded. Not only did friendship with England protect and stimulate trade between the two countries, but the misery and ruin of France also contributed to extend the commerce of the great towns just over the frontier whose trade and industries were unmolested. In 1435 Philip concluded the treaty of Arras with Charles VII, King of France, by which, for the sake of peace, the French King ceded to him a number of counties in France and made him, during his lifetime at least, an independent prince owing no homage to the French Crown. This treaty naturally enraged the English, who at once declared war on Burgundy, destroying many Burgundian vessels and raiding its coast towns. In revenge Duke Philip marched on Calais with an army of thirty thousand Flemings whom he induced to join in the war against their ancient ally chiefly through their confidence in his good intentions and against their own better judgment. The siege proved to be a long one, and the Flemings becoming discontented finally set fire to their camp and crying, "_Go, go, wy zyn all vermanden!_" ("Go, go, we are all betrayed!") marched back to Flanders, leaving their Duke raging at his discomfiture. This fiasco determined Philip to adopt a new policy toward the communes and compel them to obey his orders. On May 22, 1437, he camped outside of the city of Bruges with a considerable force of knights and Picard footmen, informing the burghers that he was on his way to Holland. The next day, telling his men "That is the Holland we have come to conquer!" as he pointed to the city, Philip led his forces to the market-place. The tocsin in the old belfry instantly sounded the alarm, and angry guildsmen and burghers came pouring down the narrow streets in thousands. Philip's small force, taken at a disadvantage, was forced to retreat to one of the gates. It was shut, its heavy bolts securely drawn. Already some of the French force had been killed, and in a few moments the Duke himself would have perished but for Burgomaster Van de Walle, who brought a smith and broke the lock. The Duke escaped with most of his followers, but many who were caught in the rear lost their lives. This was the Bruges Vespers--to distinguish it from Bruges Matin, the year of the Battle of the Spurs.