Excerpts from Books and Wikipedia
"Since mid-July, the city had been under siege, ringed by 200,000 soldiers of the Turkish Ottoman Empire. Most of the Viennese population, along with Emperor Leopold I, had fled, leaving a garrison of 12,000 troops. . . . By September 10, the fall of the city seemed imminent. But the following day a Christian relief army appeared on the hills, led by Jan III Sobieski, King of Poland and Grand Duke of Lithuania. . . . In hindsight, the defeat at Vienna marked the end of the Muslim threat to Christian Europe and the beginning of the decline of Ottoman power." [1001 Days]