Pope St. Leo III, a Roman by birth and former Cardinal-Priest of St. Susanna, began his papacy on December 26, 795, and swiftly acted to affirm the authority and autonomy of the Holy See. Upon his consecration, Leo sent Charlemagne the keys of the Confession of St. Peter and the city's standard. In turn, Leo utilized the treasure gifted by Charlemagne to strengthen Rome’s churches and charitable institutions.
Leo’s tenure was marked by remarkable resilience. After surviving a violent assassination attempt in 799 that nearly cost him his sight and speech, Leo made a pivotal journey to seek justice and stability. His appeal to Charlemagne, and the emperor’s warm reception, led to his dramatic reinstatement in Rome with wide public support. Leo’s decision to pardon his chief assailants—pleading for exile over execution—underscored his emphasis on mercy as a papal virtue.
In 800, Leo’s most defining act occurred: he crowned Charlemagne “Emperor of the Romans” on Christmas Day, a move that resurrected the Western Roman Empire and established the precedent of papal authority in imperial coronations. This event reoriented European geopolitics and signified the pope’s role as both spiritual shepherd and kingmaker.
Pope Leo was an active ecclesiastical reformer. He worked with Charlemagne to combat the heresy of Adoptionism in Spain and played a vital role in reorganizing diocesan structures across Central Europe. He also made independent interventions in England, notably excommunicating Eadbert Praen for unlawfully claiming Kent’s throne, and reaffirming Canterbury’s primacy by revoking the pallium of Lichfield.
Leo’s governance extended into church-state conflicts. He mediated disputes in Anglo-Saxon England, including the long-standing standoff between Archbishop Wulfred of Canterbury and King Cenulf of Mercia. His diplomatic skill resolved this crisis, which had paralyzed the region’s ecclesiastical function.
In Eastern Christendom, Leo stood in solidarity with persecuted monks who opposed Emperor Constantine VI’s adulterous remarriage. Though limited by distance, he offered support and later ratified a peace agreement with Emperor Michael I, restoring ecclesiastical harmony between Rome and Constantinople.
Leo also strengthened Rome’s defenses by coordinating naval protection against Saracen incursions, assigning Corsica’s security to Charlemagne, and reclaiming Church lands.
His patronage of sacred art and architecture was substantial. Leo restored numerous Roman churches and adorned them with mosaics and other embellishments. St. Susanna, his former titular church, bore his image for centuries in a celebrated mosaic. Even in Ravenna, Leo’s influence elevated church aesthetics and piety.
Pope Leo III was a significant figure in the history of the papacy, and his contributions to the Church and to the Western world are still remembered and celebrated today. He was a strong leader and defender of the Church, and he helped to establish the authority of the Pope in the Western world and to promote the use of liturgical music and chant in the Mass.
Pope Leo III was canonized as a saint by Pope Leo XIII on July 5th, 1881. He is the patron saint of Rome and is commemorated on June 12th, the feast of Saint Leo III.