Leo III was elected pope the day after Adrian I's burial in December 795 — chosen in part because, of humble origins, he had no aristocratic faction to inflame the established Roman families. They responded by ambushing him in a procession in 799, attempting to blind him and cut out his tongue, leaving him for dead in the Forum. Miraculously recovering both faculties (and full physical strength), he fled to Charlemagne at Paderborn and was personally escorted back to Rome.
On Christmas Day 800, as Charlemagne knelt in prayer before the Confessio of St. Peter at the conclusion of the Christmas Mass, Leo placed a crown on his head and proclaimed him 'Emperor of the Romans' — and the Roman people three times acclaimed him as Augustus. The act revived the Western Roman Empire after three hundred and twenty-four years of vacancy, founded the medieval Holy Roman Empire that would continue until 1806, and decisively committed the papacy to its Western Christian European future.
Leo undertook the largest building program in Rome since Constantine and Adrian, restoring the Lateran Basilica with mosaics that survive in part, raising the great Triclinium of Leo III, and rebuilding the city walls. He died in 816 having governed the Roman Church for twenty years and having decisively shaped European Christianity.