Pope St. Sixtus III

Quick Facts

Overview

St. Leo the Great is one of the greatest popes in the entire history of the Catholic Church. Along with St. Gregory the Great and St. Nicholas I, he ranks among the most influential bishops of Rome.

He defended the Catholic faith against heresy, strengthened papal authority, guided the Church through the collapse of the Western Roman Empire, and famously met Attila the Hun, persuading him not to sack Rome.

His theological masterpiece, the Tome of Leo, became the defining document of the Council of Chalcedon (AD 451) and remains one of the most important Christological texts ever written.

Early Life

Little is known about Sixtus before becoming pope.

He served among the Roman clergy during the pontificates of: St. Boniface I St. Celestine I He became known for: theological balance, administrative wisdom, love of Church unity, devotion to the Blessed Virgin Mary.

His election came only one year after the Council of Ephesus.

Becoming Pope

Following the death of Pope St. Celestine I, Sixtus was elected Bishop of Rome on July 31, AD 432.

His first priority was healing divisions left by the Nestorian controversy.

Many Eastern bishops had struggled to accept the Council of Ephesus.

Rather than inflaming tensions, Sixtus sought reconciliation while never compromising Catholic doctrine.

Building St. Mary Major

The greatest visible legacy of Sixtus III is the Basilica of St. Mary Major.

Following the Council of Ephesus, devotion to Mary as the Mother of God spread rapidly.

To honor this truth, Sixtus extensively rebuilt one of Rome’s oldest Marian churches.

The basilica became: one of Rome’s four major papal basilicas, the oldest church in the West dedicated to the Blessed Virgin, a lasting monument to the Incarnation.

Its magnificent fifth-century mosaics still survive today and remain among the finest examples of early Christian art.

Implementing the Council of Ephesus

Sixtus worked tirelessly to ensure that the teachings of Ephesus were accepted throughout the Church.

He reaffirmed: Christ is one Divine Person.

Christ possesses both a divine and human nature.

Mary is rightly called Mother of God because she gave birth to the Person of Jesus Christ, who is God the Son incarnate.

These teachings strengthened Catholic devotion while protecting orthodox Christology.

Reconciliation in the East

After years of conflict between supporters of St. Cyril of Alexandria and former supporters of Nestorius, Sixtus encouraged peace.

His diplomacy helped support the Formula of Union (AD 433) between many Eastern bishops.

While not every division disappeared, significant reconciliation was achieved without sacrificing doctrine.

Historical Context

Roman Emperors Valentinian III (West) Ruled the Western Empire during increasing barbarian pressure.

Theodosius II (East) Continued supporting the Church while navigating complex theological disputes.

The Church

During Sixtus’ pontificate: The Council of Ephesus was fully implemented.

Marian devotion expanded.

Rome experienced a period of peace.

Great churches continued to be built.

Papal authority continued growing.

Major Contributions

• Forty-fourth Pope of the Catholic Church
• Implemented the Council of Ephesus
• Rebuilt the Basilica of St. Mary Major
• Promoted devotion to Mary as Mother of God
• Encouraged reconciliation after the Nestorian controversy
• Strengthened the unity of the Church

Interesting Facts

• The mosaics commissioned during his pontificate still survive.
• St. Mary Major remains one of the most important Marian churches in the world.
• His pontificate bridged the age of Ephesus and the age of Leo the Great.

Legacy

Pope St. Sixtus III transformed theological victory into visible Catholic life. Through sacred architecture, careful diplomacy, and pastoral leadership, he ensured that the truths proclaimed at Ephesus became part of the Church’s worship and devotion. His work reminds Catholics that doctrine is meant to be lived, celebrated, and proclaimed through both faith and beauty.

Pope #45

St. Leo I (“Leo the Great”) The Forty-Fifth Pope of the Catholic Church “Thou art Peter; and upon this rock I will build my church.” – Matthew 16:18 (Douay-Rheims)

Early Life

Leo was born in Tuscany around AD 390.

He quickly became known as: an outstanding preacher, gifted theologian, skilled diplomat, trusted adviser to emperors.

Before becoming pope he had already served as one of the Church’s leading deacons.

Becoming Pope

Leo was elected Bishop of Rome while serving on an imperial diplomatic mission.

His reputation was so respected that the clergy unanimously chose him despite his absence.

He was consecrated on September 29, AD 440.

The Tome of Leo

The defining theological achievement of Leo’s pontificate was the Tome of Leo.

Written to Patriarch Flavian of Constantinople, it explained that Jesus Christ is: one Divine Person, possessing two complete natures, fully God, fully man, without confusion, without change, without division, without separation.

This document became the theological foundation of the Council of Chalcedon (AD 451).

When it was read aloud, the bishops famously cried: “Peter has spoken through Leo!” Few statements in Church history better illustrate the respect shown to the Bishop of Rome during the early Ecumenical Councils.

The Council of Chalcedon (AD 451)

The Fourth Ecumenical Council condemned Eutychianism (Monophysitism) and reaffirmed: Christ possesses: one Divine Person, two complete natures, divine and human.

This definition remains Catholic doctrine today.

Meeting Attila the Hun

One of history’s most famous papal encounters occurred in AD 452.

Attila and his armies marched toward Rome.

Instead of sending an army, Leo went personally.

The exact conversation is unknown.

Ancient tradition holds that Attila unexpectedly withdrew after meeting the pope.

Some traditions even report Attila saw Sts. Peter and Paul standing beside Leo with drawn swords.

Whether legendary or historical, the undeniable fact remains: Attila turned back.

Rome was spared.

Saving Rome Again

In AD 455, the Vandals under Genseric entered Rome.

Leo again negotiated personally.

Although the city was looted, his intervention prevented: widespread massacre, systematic destruction, large-scale burning.

Even pagan historians admired his courage.

Defender of Papal Primacy

Leo wrote extensively about the authority of the Bishop of Rome.

He taught that: Peter continues his ministry through his successors.

The pope serves the unity of the universal Church.

Rome possesses a unique responsibility among all Churches.

His writings became foundational for Catholic teaching on the papacy.

Historical Context

During Leo’s pontificate: The Western Roman Empire neared collapse.

Attila invaded Italy.

Chalcedon defined orthodox Christology.

Barbarian kingdoms spread across Europe.

Rome increasingly looked to the pope rather than the emperor for leadership.

Major Contributions

• Forty-fifth Pope
• Doctor of the Church
• Wrote the Tome of Leo
• Guided the Council of Chalcedon
• Met Attila the Hun
• Protected Rome twice
• Strengthened papal primacy
• One of history’s greatest theologians

Legacy Scorecard

Interesting Facts

• First pope officially called “the Great.”
• Doctor of the Church.
• His sermons are still read today.
• Personally confronted Attila the Hun.
• His Christology remains Catholic teaching.
• One of the greatest Latin Fathers of the Church.

Legacy

Few men have shaped Catholic history more profoundly than St. Leo the Great. He preserved orthodox doctrine at Chalcedon, defended the authority of the Apostolic See, protected Rome from destruction, and guided the Church as the Western Roman Empire crumbled around him. Through his preaching, diplomacy, and theological brilliance, Leo demonstrated that the pope is called not only to teach but also to courageously shepherd the Church during times of immense crisis.

Sources and Further Study

See the source notes preserved in the supplied CatholicG33k biography and the batch audit record for this page.

Timeline

Papal Legacy Scorecard