The War of the Spanish Succession was Europe's great dynastic gamble. When the last Habsburg king of Spain died without an heir in 1700, two rival claimants emerged: Philip, a French Bourbon prince backed by Louis XIV, and Archduke Charles of Austria, supported by England, the Dutch Republic, and the Holy Roman Empire through the Second Grand Alliance. The war that followed engulfed the continent, but its resolution in Spain depended on cities choosing sides. Barcelona was the key to Catalonia, and Catalonia was the key to the eastern half of Spain. To take Barcelona, the Alliance first needed Montjuic. English general Charles Mordaunt, the 3rd Earl of Peterborough, landed his multinational force on the Catalan coast on 22 August 1705, knowing that the fortress on the hill above the city stood between him and his objective.

George of Hesse-Darmstadt, a German prince who had served as the last Habsburg viceroy of Catalonia, led the initial approach late on the night of 13 September. He knew the terrain from his years governing the region, and he understood that surprise was the only advantage his force held against the castle's Neapolitan and Spanish garrison, men loyal to the Bourbon claimant Philip V. Darmstadt's Austrian troops moved uphill in darkness, their progress masked by the sounds of the Mediterranean wind and the city below. Lord Peterborough brought up the main body behind them. When the outer defenses were reached, the fighting was brutal and close. Darmstadt was mortally wounded in the assault and died on the hillside, one of the first casualties of the battle he had planned. The defenders fought back, and the initial assault faltered, men retreating downhill before Peterborough rallied them. They took the outer works, but the inner castle held, and the garrison prepared for a prolonged siege.

Fighting continued for four days, the Alliance forces tightening their grip on the fortress while the Neapolitan garrison fought with the desperation of men who knew that losing the castle meant losing the city. On 17 September, a mortar round directed by Dutch Colonel Schellundt found the castle's powder magazine. The explosion killed the Neapolitan commander, Colonel Carracciolo, along with several officers, and shattered both the magazine and the garrison's will to resist. The fortress fell. With Montjuic gone, Barcelona's defenses crumbled, and the city soon declared for Archduke Charles. Catalonia's support for the Habsburg pretender ran deep, rooted in a historical memory of greater autonomy under the Aragonese crown. The Catalans were not fighting for Charles out of abstract loyalty; they were fighting against a Bourbon centralism that threatened their traditional rights and institutions.

The capture of Montjuic in 1705 opened Barcelona to the Grand Alliance and gave Archduke Charles a capital from which to press his claim. For a time, it seemed the gamble would pay off. But the war ground on for another nine years, and when it ended with the Treaty of Utrecht in 1713, Charles had been abandoned by his allies, who decided that a Bourbon Spain was acceptable after all. Barcelona held out until September 1714, enduring a fourteen-month siege before finally falling to Philip V's forces. The new Bourbon king punished Catalonia harshly, abolishing its autonomous institutions through the Nueva Planta decrees. The victory at Montjuic, which had seemed to promise Catalan self-governance under a sympathetic Habsburg, led instead to the most severe centralization the region had ever experienced. The hill that had offered hope became, once again, a symbol of what was lost.