Why Did Pope Leo III Crown Charlemagne the First Holy Roman Emperor?

Pope Leo III crowned Charlemagne Emperor of the Romans on Christmas Day, 800. His coronation was the culmination of years of mutual support between Charlemagne and the Holy See, and shored up a mutually beneficial relationship. By crowning Charlemagne, Leo gained military support for the Vatican, and Charlemagne gained the authority to revive the unity of the Roman Empire in medieval Europe.

Charlemagne, or Charles the Great, was the king of the Franks -- a medieval Germanic tribe whose territory covered modern-day Belgium, France, the Netherlands, Luxembourg and western Germany. His goal was to unite all the Germanic tribes through militaristic action and then bring peace and stability to his territory -- which was the largest united territory since the fall of the Roman Empire -- by reviving the Greco-Roman past, converting the Germanic tribes to Christianity and preserving the Germanic way of life.

Pope Leo III was born a commoner and worked his way up to Cardinal-Priest of one of the oldest churches in Rome, as well as chief of the pontifical treasury before he was elected pope in 795. Leo's election occurred in haste; he was chosen to be the pope on the same day his predecessor, Pope Adrian I, was buried. Leo was then consecrated the following the day. From the start, he faced opposition in Rome prompted by jealousy and a disdain from certain factions that believed only a noble should hold the office of pope.

One of Leo's first acts as pope was to send Charlemagne the keys to St. Peter's and the standard of the city of Rome in 795. Charlemagne responded with congratulations and a gift of a large treasury that Leo used to fund charities in Rome. Charlemagne's willingness to defend the Church was established by Pope Adrian I, who requested his help to defeat the Lombard King Desiderius when he marched on the Papal States. When political adversaries attacked Pope Leo III in Rome in 799, he nearly died, surviving only to be imprisoned in a monastery. Escaping, he fled to Charlemagne in Paderborn, Germany. Charlemagne placed Leo's attackers under arrest and sent an armed escort with the pope back to Rome.

In 800, Charlemagne traveled to Rome accompanied by the conspirators who attempted to kill Pope Leo III. Leo granted them a stay of execution and sentenced them to exile. A few days later, Leo crowned Charlemagne during Christmas mass. Through this act, Leo and Charlemagne cemented a mutually beneficial relationship between the Church and state authority. Although historians debate the exact symbolism of Charlemagne's coronation, there is no doubt that Pope Leo recognized the need of the Holy See to be backed up by military authority, which Charlemagne could provide. Charlemagne also discerned that the Church was necessary to unify the various Germanic tribes in his empire, help establish his authority over those tribes and revive the law and infrastructure of the Roman empire, which was one of the goals of his reign. Through the crowning of Charlemagne, both men gained authority and power in their respective roles.