Maximilian II Emanuel, Elector of Bavaria, expected something easier. He had once governed the Spanish Netherlands and believed the people of Brussels still loved him. The city's medieval fortifications were notoriously outdated. The Allied army under the Duke of Marlborough was tied up dozens of miles away besieging Lille, and the garrison left to hold Brussels was only six battalions strong, drawn from Dutch, Imperial, British, Saxon, and Southern Netherlandish regiments. Maximilian rode toward the city with fifteen thousand mostly French troops in November 1708, sure that civilians would open the gates the moment he summoned the governor. He had been told the assault would be a formality.

The Duke of Marlborough had spies who were very good at their work. Almost as soon as the Bavarian's plan was conceived in Marshal Vendome's tent, the Allies knew about it. Reinforcements quietly slipped into Brussels. Two Dutch deputies, Johan van den Bergh and Frederik van Renswoude, made sure the garrison was paid in full and well fed — small acts of administrative competence that matter immensely to the morale of men about to be shot at in the cold. By the time Maximilian's deputy, the Comte d'Arco, drew up his troops outside Brussels on November 22, the city's defenders included nine battalions, a Southern Netherlands dragoon regiment, and four hundred Imperial hussars under the resolute Governor Francois de Pascale. When Maximilian sent his summons to surrender, Pascale said no.

Maximilian had no siege artillery with him. It had to be hauled in from Mons, which took days. The attackers spent the freezing night of November 24th opening trenches on the southeastern side of the city. On the morning of November 26 they finally opened fire with eight cannons and four mortars — and the defenders' guns silenced them within hours. That evening, the French tried infantry. After eight in the evening, six thousand French soldiers stormed the covertway. What happened next was not the story Maximilian had been told to expect. Brussels civilians, instead of opening the gates, brought weapons to the palisades and fought alongside the garrison. Nine French assaults broke against them through the long night. By nine the next morning Pascale himself led a cavalry sortie out of the city, scattering the attackers and pushing forward to seize their guns.

The defenders steeled themselves for one more horror that night: heated shot, fired into the wooden roofs of the medieval city to start fires and provoke panic. It never came. Around midnight, scouts crept out and discovered the unbelievable. The French had quietly withdrawn. They left behind 17 cannons, 2 mortars, and many of their wounded — the unmistakable signature of an army that had run out of options. Pascale led the cavalry in pursuit. The reason for the sudden Bavarian retreat lay far to the west. Marlborough and Prince Eugene had forced the Scheldt River at Kerkhoff and Gavere with pontoon bridges, catching the French defenders of the river line completely flat. The whole French strategic position collapsed overnight; Maximilian's exposed position outside Brussels became untenable, and he fled to Mons.

The assault cost the French about 2,500 men. The Allies lost roughly 400 — the small print of an 18th-century military campaign, names mostly unrecorded, families never told. Twelve days later, on December 9, the citadel of Lille surrendered to Marlborough, and the great French marshal Boufflers was allowed to march his survivors out with full honours. Marlborough kept campaigning into the freezing dark of December, taking Ghent on December 30 and Bruges soon after. Then the worst winter in living memory descended on Europe — the Great Frost of 1709 — and Louis XIV, his treasury drained and his army demoralised, sent diplomats to negotiate peace. The Sun King's pride could not quite swallow the Allies' terms, so the war ground on for years more. But the November when Brussels civilians chose to fight beside their garrison rather than open the gates — that night had already changed the map.