"When Turkish forces that had already conquered Belgrade besieged Vienna for two months in 1683, D'Aviano, at the behest of Pope Innocent XI, joined the irresolute Leopold outside Vienna, where he strengthened the emperor's resolve, persuaded the divided and outnumbered Christian forces to choose Jan Sobinski, the Polish king, as their leader, and preached to the Catholic-Protestant-Orthodox forces on the importance of defending Christian Europe. On the night of September 11, 1683, the Christians forced the Turks, 20,000 of whose troops had been killed, to raise the siege. "