Pope Leo is most noted for protecting Charlemagne from his enemies in Rome and crowning him Holy Roman Emperor as well as “Augustus of Rome.”
Leo was born into a modest family in the countryside around Rome. His parents were Aliguppius and Elizabeth. Little more is known of his youth. The fact that he was born into a non-noble family played havoc with his career, later. Becoming a priest, Leo worked his way up the ranks of the Church, eventually becoming the cardinal-priest of Santa Susanna as well as the treasurer of the Church.
The day after Christmas, 795, the day Pope Adrian was buried, Leo was elected unanimously by the nobles and priests of Rome. Fear of the Lombards acting on the news of Adrian’s death may have hastened the election. The Lombards, of which there were a number of partisans in Rome, could have intervened in the voting.
Leo almost immediately sent a letter to Charlemagne to inform him of the results. He also sent the king the keys to the confession of St. Peter plus a standard of the city. Leo also requested an envoy. The implication of this was obvious: Charlemagne was seen to be the protector of the Holy See. In response, Charlemagne sent a letter on congratulations and a large portion of the treasure he had captured from the Avars (approximately Ukraine, Kazakhstan and western Russia). However, he made it understood that his function was to defend the Church and Leo’s function was to pray for the realm and victories for the Frankish army.
The Roman nobles were not happy with a commoner as pope. They plotted, brought up various accusations, and on 25 April 799, they got their chance. During a procession, Leo was attacked, left injured and unconscious, and sent to a monastery. After recovering, Leo escaped and crossed the Alps to find Charlemagne at Paderborn. The king took it upon himself to negotiate with the Roman nobles, thereby regaining the throne for Leo. But by November, 800, the problems raised their heads again and Charlemagne had to travel to Rome. The first half of December saw a trial whereby Leo was acquitted of all after taking an oath to affirm his innocence of all accusations.
On Christmas Day, Charlemagne, not expecting this, supposedly, was crowned emperor of the Holy Roman Empire. This, in essence, divided the weak Roman Empire, centered in Constantinople, in half. The empress was too powerless to object. Almost immediately, Charlemagne began his successful attempts to improve education and culture in the new empire.
Leo committed Corsica to Charlemagne for safekeeping, due to the Muslim raids on that island. Apparently, the emperor was busy. The Muslims continued to occupy the place.
However, Charlemagne seemed to want to take over the Eastern Empire. The long-standing argument about the addition of the filoque to the Nicene Creed was the pivot point. The decision of the Council of Aachen of 809 to add the filoque was opposed to the Eastern Church’s refusal to use it. Accusing the Eastern Church of heresy would be Charlemagne’s impetus to declare war. Leo did not want war, so he forbade the use of the filoque and actually put up two silver shields with the words (minus that phrase) of the Nicene Creed in St. Peter’s.
Due to the treasure that Charlemagne gave Leo, the pope had sufficient money to beautify Rome during his pontificate. He also helped restore King Eardwulf of Northumbria, who had been deposed.
Charlemagne died in 814. The Roman nobles reasserted their hate of Leo and he had to deal with the conspirators during the remaining year and a half of his reign.
He died June 12, 816. Pope Clement X had Pope Leo canonized in 1673.
Leo will be known for promoting a vision of the Christian world as a single, orderly, peaceful society under the ultimate authority of the Bishop of Rome as Christ’s deputy on earth.