The Mayor of Paris, Jean Sylvain Bailly, is forced to declare martial law after Danton and his supporters gather at the Champ de Mars. Initially dispersed, they returned on 17 July, 1791, gathering souvenirs, banners, and flags. However, the National Guard also returns, and after firing a warning shot, the crowd throws stones at the soldiers. Taking this as a sign of hostility, Bailly orders his troops to open fire, despite Lafayette's efforts to maintain peace between both sides. The resulting massacre is a bloodbath, with dozens dead or wounded. The survivors quickly scatter. A few weeks later, Louis XVI and the National Assembly declare war on the great powers of Europe, but Robespierre knows that the campaign will be a disaster. French troops march on the Belgian frontier, but are quickly annihilated by forces of Prussia and Austria. Jean-Paul Marat demands that "ten thousand heads must fall here in France." The Duke of Brunswick issues a proclamation demanding that France surrender, or he will "burn Paris to the ground." Another call to action is given at the National Assembly, with Robespierre again certain that the next campaign will be a disaster. While French soldiers make their way to the front, they are given provisions in the towns they enter.