(c. 750-816) Pope from 795. After the withdrawal of the Byzantine emperors, the popes had become the real rulers of Rome. Leo III was forced to flee because of a conspiracy in Rome and took refuge at the court of the Frankish king Charlemagne. He returned to Rome in 799 and crowned Charlemagne emperor on Christmas Day 800, establishing the secular sovereignty of the pope over Rome under the suzerainty of the emperor (who became the Holy Roman emperor).