Pope Leo III is attacked by supporters of his predecessor, Pope Adrian I. Known to history as "Charlemagne's Pope" because he crowns Charlemagne as Emperor of the Holy Roman Empire on Christmas Day, 800 CE, he was elected unanimously and is liked by other bishops.
However, his family is not nobility and this upsets the noble families in Rome — as far as they are concerned, the papacy is a position of great power and should be reserved for the nobility.
They therefore keep accusing him of various crimes, including adultery, and on this day a gang of "nobles" attempts to gouge out his eyes and cut off his tongue. He's saved, but then deposed, and that's when he goes to Charlemagne who takes his side. When Charlemagne travels to Rome in support of Pope Leo III, that's when Leo crowns him emperor.