The Ottoman Threat and the Scale of the Siege: In September 1683, Vienna came under the threat of the Ottoman Empire, which sought to expand its influence into Central Europe . Kara Mustafa Pasha's army was one of the largest Europe had seen in a century, numbering perhaps 150,000 soldiers, including elite units of Janissaries, spahis cavalry and fearsome Tartars . The siege began on July 14, 1683, and the Turks' goal was to capture the city not by storm, but by hunger and fear , . Defense of the City : Emperor Leopold I fled the city on July 7, leaving Vienna in the hands of a garrison of only 15,000 soldiers and 5,000 civilian militia . The defense of the city, despite lack of food, disease and constant bombardment, was led by Count Ernst Rüdiger von Starhemberg, who kept the morale of soldiers and civilians , . Formation of the Holy League : Faced with the threat, Pope Innocent XI regarded the siege of Vienna as the most serious threat to Christianity since the fall of Constantinople and called on European rulers to form the Holy League , . The Pope succeeded in convincing King Jan III Sobieski of Poland to commit his forces to the defense of Vienna, offering financial and diplomatic support . Sobieski, a veteran known for his strategic genius, declared that saving Vienna was tantamount to saving Poland . The Holy League was a coalition consisting of Polish troops, contingents from Bavaria, Saxony, Franconia and Swabia, and forces of the Holy Roman Empire, totaling about 70,000 troops , . Decisive Battle of Vienna: The allied army, led by Sobieski, reached the hills overlooking Vienna on September 10, and the battle took place on September 12, 1683 . Kara Mustafa Pasha, despite his huge forces (about 120,000), was overconfident and underestimated the determination of the defenders and the bravery of the Polish king . Sobieski coordinated the actions of the allies, hiding his movements in the wooded hills and keeping 20,000 Polish cavalry on the right wing in reserve, waiting for the decisive moment , . Hussar Charge: When the Ottoman lines began to weaken under infantry pressure, Sobieski ordered a charge that was the largest cavalry attack in European history , . Nearly 20,000 horsemen took part in the charge, led by Polish hussars, whose wings of eagle feathers emitted a "ghostly hiss," spreading fear among the enemy , . The mass and momentum of the charge shattered the Ottoman ranks "like a bolt from the blue," and Pasha's troops fell into chaos and began a full retreat , . Consequences of Victory: The victory, which followed the complete crushing and retreat of the Ottoman army, was a turning point in European history, stopping Ottoman expansion into Central Europe , . Sobieski was hailed as a hero, and the city of Vienna, despite its destruction, regained its vitality , . The battle strengthened alliances in Christian Europe (the Holy League), demonstrating that unity, strategy and courage could defeat overwhelming forces , . The memory of the hussar charge and Sobieski's command was immortalized, shaping diplomacy, war and the balance of power for decades , .