In the year 590, when Saint Gregory the Great was elected pope, Rome and all of Italy was in the midst of a deadly plague. In fact, Pope St Gregory was elected because his predecessor, Pope Pelagius, himself died of the epidemic on Feb 7th, 590. On April 25 of that year, the holy pope St Gregory requested a public procession through the streets of Rome to beg for an end to the epidemic. An icon of Our Lady that was painted by Saint Luke the Evangelist was carried at the head of the prayerful entourage.
As the procession wound along the Tiber River, the Litany of Saints was intoned. At the conclusion of the litany, Saint Gregory’s gaze was drawn upwards and he suddenly saw the heavens open. Saint Michael the Archangel along with numerous other Angels descended above the crowd and a heavenly perfume seemingly filled the air. The angels began singing the “Regina Coeli” to the Blessed Virgin Mary, who was seated on a throne above Michael and the Angels
Completely overwhelmed by the incredible sight, Saint Gregory concluded the angelic chorus by singing out the closing lines of the Regina Coeli: “Ora pro nobis Deum, alleluia! Gaude et lætare, Virgo Maria, alleluia! Quia surrexit Dominus vere, alleluia.” (Pray for us to God, alleluia! Rejoice and be glad, O Virgin Mary, alleluia! For the Lord has truly risen, alleluia!).
At the conclusion of the vision, the great pope witnessed Saint Michael sheathing his sword, and to the great joy of all the inhabitants the horrific plague came to an end. The beautiful Church called Castel Sant’Angelo stands at the site where Saint Michael and his fellow angels had appeared on that day along with the Blessed Virgin Mary.
From then on, the date of the apparition (April 25th) marking the end of the plague thus became the fixed date for the annual procession that would come to be known throughout the Catholic world as the “Greater Litanies”, since it was St Michael along with the Angels who joined in reciting the Litanies on that day. Nowadays the “Greater Litanies” processions are sometimes called “St Mark’s processions” because the date also coincides with the feast of St Mark.