More than fifteen hundred years ago, the great Roman Empire was growing old and tired. Its walls were cracking, its soldiers were few, and warrior peoples from faraway lands were crossing its borders. In those troubled times lived a man named Leo, born in Tuscany, a region of green hills in the heart of Italy. He became a deacon in Rome and grew famous for his wisdom: whenever there was a difficult quarrel, it was Leo they sent for to calm everyone down.

In the year 440, the people and clergy of Rome chose him to be pope. Leo took his mission seriously from the very first day. He preached in a clear, steady voice, and his sermons were so beautiful that people copied them out by hand to keep. Nearly one hundred of those sermons, and about one hundred and fifty of his letters, still exist today.

In those days, many people were confused about who Jesus really was. Some said he was only God, pretending to be a man. Others said he was only a very good man. So Leo wrote a famous letter to Bishop Flavian, calmly explaining the faith of the Church: Jesus is true God and true man at the same time. Truly God, able to heal and to forgive; truly man, able to feel hunger, tiredness, and tenderness.

In the year 451, bishops from all over the world gathered for a great council in the city of Chalcedon, far away from Rome. When Leo's letter was read aloud, the bishops rose to their feet and cried out together:

— Peter has spoken through the mouth of Leo!

It was their way of saying that the pope, the successor of Saint Peter, had taught the truth. That letter became known as the Tome of Leo, and the Church treasures it to this day.

But Leo's hardest test was still to come. In the year 452, news reached Rome that froze every heart: Attila, king of the Huns, had invaded Italy. The Huns were swift and fearsome horsemen, and wherever they passed they left cities in ruins. Aquileia, one of the greatest cities of the north, had been destroyed. People said that where Attila's horse set its hoof, the grass never grew again.

Rome trembled. The emperor's army was far too weak to face the Huns, and families were already packing their belongings to flee. Then the Romans decided to try one last thing: they would send an embassy of peace. And the one who would ride at its head, with no sword and no shield, was Pope Leo.

Leo traveled north for many days, accompanied by two Roman noblemen. He went to meet Attila near the city of Mantua, by the waters of the river Mincio, where the Hun army lay camped. On one side stood thousands of armed warriors. On the other, a gray-haired man in pale robes, mounted on a gentle horse.

The two of them spoke face to face. No one wrote down the exact words Leo said, but everyone saw what happened next: Attila, the warrior no army had been able to stop, ordered his troops to turn around, and he left Italy in peace. Rome was saved without a single arrow being fired.

An old tradition tells that during their talk, Attila saw two majestic, shining figures standing beside the pope, with swords raised against the sky: Saint Peter and Saint Paul, protecting Rome and its shepherd. Frightened, the king of the Huns is said to have decided at that very moment to retreat. However it happened, the whole world understood that Leo's gentle courage had done what no wall ever could.

Three years later, in 455, another threat arrived: Genseric, king of the Vandals, landed near Rome with his warships. This time there was no way to keep the army out of the city. Once again Leo went out to meet the invader, unarmed, and pleaded for his people. He could not win everything, but he won a great deal: Genseric promised not to burn the city and not to harm its people. The great basilicas were left standing, and inside them many families found safe shelter.

Leo spent the rest of his life caring for his flock, teaching, helping the poor, and rebuilding what the wars had knocked down. He died on the tenth of November in the year 461, after more than twenty years as pope, and he was buried close to the tomb of Saint Peter, the fisherman he loved so much.

The people never forgot him. He was the first pope in history to receive the title "the Great." And many centuries later, the Church declared him a Doctor of the Church, a master of the faith whose teachings are still alive today. All because of one man who faced the most fearsome armies in the world armed only with faith, words, and peace.