Pope from 795. After being attacked in Rome in 799, Leo fled to Charlemagne, who provided him with an escort. When Charlemagne came to Rome, the Pope crowned him Holy Roman Emperor (800). At Charlemagne's instigation he took strong measures against the Adoptianist heresy. He intervened in the differences between the Abps. of Canterbury and the Anglo-Saxon Kings, and in the E. he encouraged the monks in their opposition to the Emp. Constantine VI. Feast day, 12 Jun.