Christians in the fifth century called Attila, war leader of the Huns, "the Scourge of God." He has become an almost mythical figure. Richard Wagner was so taken with the warrior's exploits that his famous opera cycle, The Ring of the Nibelung, was based on the story of Attila's battle with the Burgundian king, Gundahar, along with other historical figures like Queen Brynhild.
Attila invaded Italy in 452 CE. When the city of Aquileia fell to his army, the road was open all the way to Rome. The empire was by this time divided into West (governed by Rome) and East (governed by Constantinople). The Roman West was weak, both in character and in military strength. The Eastern empire left no doubt that they did not want to intervene. So Leo "the Great," who has been called the first pope in the modern sense, went to talk to Attila personally.
One of history's mysteries occurred at that meeting. No one knows what was said between the two leaders. Legends later reported that Attila had a vision of Saints Peter and Paul marching with the pope. Whatever he saw, Attila decided not to attack Rome. He turned north instead and died shortly thereafter.
Leo was still Bishop of Rome when Vandals attacked in 455. He was unable to prevent the sacking of the city. But he was able to arrange a treaty with them, so at least the city was not burned to the ground.
Such negotiations helped Leo's reputation and gave him great political and spiritual clout. Lost to history is the substance of the sermon that made Attila, "the Scourge of God," see the light.