Memorial plaque to Polish king Jan III Sobieski, mounted on the wall of St. Josef church on Kahlenberg.

In July 1683, roughly 150,000 Ottoman troops laid siege to Vienna, the capital of the Holy Roman Empire. Emperor Leopold I (r. 1658-1705) fled the city. Alarmed by this threat to Christian Europe, Pope Innocent XI asked Polish king Jan Sobieski (r. 1674-96) to come to Vienna's aid.
Sobieski agreed and joined Charles of Lorraine, the electors of Saxony and Bavaria, and numerous German princes in an alliance against the Turks. The combined relief army of approximately 80,000 troops consisted of roughly 27,000 Polish soldiers (among them 3,000 highly trained “Winged Hussars”); 19,000 Austrians; 10,500 Bavarians; 9,000 Saxons; and 9,500 soldiers from the southwestern German principalities.
Under Sobieski's command, imperial forces scored a decisive victory over Ottoman troops at the Battle of Kahlenberg on September 12, 1683, and thereby lifted the siege. The people of Vienna embraced Sobieski as their liberator.