An event occurred in the reign of Constantine which paved the way for the partial jurisdiction which the Roman Pontiffs commenced to enjoy over Rome, and which they continued to exercise till they obtained full sovereignty in the days of King Pepin of France.
In the year 327 the Emperor Constantine transferred the seat of empire from Rome to Constantinople, the present capital of Turkey. The city was named after Constantine, who founded it. A subsequent emperor appointed a governor, or exarch, to rule Italy, who resided in the city of Ravenna. This new system, as is manifest, did not work well. The Emperor of Constantinople referred all matters to his deputy in Ravenna, and the deputy was more anxious to conciliate the Emperor than to satisfy the people of Rome. Italy and Rome were then in a political condition analogous to that in which the Irish were placed for several centuries.
Abandoned to itself, Rome became a tempting prey to those numerous hordes of Barbarians from the North that then devastated Italy. The city was successively attacked by the Goths under Alaric, and by the Vandals under Genseric, and was threatened by the Huns under Attila. Unable to obtain assistance from the Emperor in the East, or the Governor at Ravenna, the citizens of Rome looked up to the Popes as their only Governors and protectors, and their only salvation in the dangers which threatened them. The confidence which they reposed in the Pontiffs was not misplaced. The Popes were not only devoted spiritual Fathers, but firm and valiant civil Governors. When Attila, who was surnamed "the Scourge of God," approached the city with an army of 500,000 men, Pope Leo the Great went out to meet him unattended by troops. His mild eloquence disarmed the indomitable chieftain and induced him to retrace his steps. Thus he saved the city from pillage and the people from destruction. The same Pope Leo also confronted Genseric, the leader of the Vandals; and although he could not this time protect Rome from the plunder of the soldiers he saved the lives of the citizens from slaughter. Such acts as these were naturally calculated to bind the Roman people more strongly to the Popes and to alienate them from their nominal rulers.