The Church, around the 5th century, had a particular need for the protection of St. Michael: the barbarians arrived, the Roman Empire collapsed under their attacks and the new beginning was charged with thunderstorms. To guard Rome, the seat of the Papacy, St. Michael descended to a peninsula of Italy at the border of the Adriatic Sea, in front of the Orient— the cradle of heresies and the land of the Saracens who would be for a long time the terror of civilised Europe.
A rich man from Siponte noticed the disappearance of an ox from his herd while he was bringing them to graze on the sides of Mount Gargano. He sought it, and found it at the summit of the mountain, at the entrance of an inaccessible cavern. He shot an arrow at the ox, but, o the prodigy! The arrow returned and injured himself. The man consulted the Bishop who ordered prayers and fastings. Then the Prince of the Angels appeared and told him: “I am the Archangel Michael. I have chosen this place for my honour, I will be the Protector and Guardian forever.” The Sipontians come in crowds to see this blessed place. “He who has built this shrine,” said the Archangel to the Bishop, “he himself consecrates it. You will see a sign of the miraculous consecration.” On entering the grotto, the Bishop found a purple coat and recognized it as the place where the Archangel placed his foot.
The Church remembers this apparition on the 8th of May.
We beg you, invincible Prince, help the people of God and give them victory! This people venerates you as their protector and their patron, the Church prides herself on having you to defend against the powers of Hell. To you, God has granted the care of conducting the armies of the Celestial Beatitude. Pray, therefore, the God of peace to put under our feet, Satan, defeated and downcast, that he may no longer restrain men in slavery nor cause harm to the Church. Amen.
(Taken from a prayer composed by Pope Leo XIII)