Leo, a Cardinal and Roman native, was unanimously elected Pope upon the death of Adrian I. His predecessor had tried to keep the papacy independent of the power struggles taking place between the Eastern Empire and the western kingdoms, but Pope Leo immediately threw his support behind Charlemagne. He recognized the Frankish king as protector of the city, sending tokens of good will and receiving treasure for the papacy in return.

An opposing faction led by a nephew of Adrian, either out of jealousy or dissatisfaction with the pope's alliance with Charlemagne, accused Leo of misconduct, perjury and adultery. In April of 799, assailants incited by this faction attacked Pope Leo in the streets of Rome with the goal of blinding him and cutting out his tongue. Such mutilations would have made Leo unfit to continue as pope.

However, Leo escaped and fled to the protection of Charlemagne at Paderborn. Precisely what, if any, negotiations took place remains unknown, but shortly thereafter Pope Leo returned to Rome under a safe escort. In November, a commission controlled by the Frankish king arrested and deported Leo's assailants and discredited the accusations that had been made against him.

Still, unrest prevailed in Rome and Leo's position was unstable. Charlemagne himself came to the city in the fall of 800 to restore order, and on December 23 Leo officially purged himself of the charges against him in the presence of the king.

Two days later, at a mass in St. Peter's Basilica, Pope Leo unexpectedly crowned Charlemagne Emperor.

Although it was a surprise to Charles, Leo had obviously planned this (the assembly broke into shouts of "Charles, the most pious Augustus, crowned by God"). The action had no foundation in canon law and was revolutionary; it established the significant precedent that only the pope could confer the imperial crown, tied the Church closely to the Carolingian empire, and widened the schism between the Eastern and Western churches.

The rest of Leo's pontificate was relatively uneventful. His relationship with the empire was amiable; the Carolingians exerted some influence on ecclesiastical matters but Leo proved diplomatically adept and stood fast on matters of doctrine. He suffered from a resurgence of trouble with the Roman nobility toward the end of his pontificate, but nothing drastic came of it.

Pope Leo III died in 816 and was made a saint in 1673. He is sometimes referred to as "Charlemagne's Pope."

Who's Who Profile of Pope Leo III