On Pope Leo XIII's Prayer To St. Michael

In 1947 Father Domenico Pechenino related what he had witnessed over six decades before.

“I do not remember the exact year. One morning the great Pope Leo XIII had celebrated a Mass and, as usual, was attending a Mass of thanksgiving. Suddenly, we saw him raise his head and stare at something above the celebrant’s head. He was staring motionlessly, without batting an eye. His expression was one of horror and awe; the colour and look on his face changing rapidly. Something unusual and grave was happening in him.

“Finally, as though coming to his senses, he lightly but firmly tapped his hand and rose to his feet. He headed for his private office. His retinue followed anxiously and solicitously, whispering: ‘Holy Father, are you not feeling well? Do you need anything?’ He answered: ‘Nothing, nothing.’ About half an hour later, he called for the Secretary of the Congregation of Rites and, handing him a sheet of paper, requested that it be printed and sent to all the ordinaries around the world. What was that paper? It was the prayer that we recite with the people at the end of every Mass. It is the plea to Mary and the passionate request to the Prince of the heavenly host, (St. Michael: Saint Michael the Archangel, defend us in battle) beseeching God to send Satan back to hell.”

Cardinal Giovanni Batista Nassalli Rocca di Corneiliano wrote in his Pastoral Letters on Lent: “the sentence ‘The evil spirits who wander through the world for the ruin of souls’ has a historical explanation that was many times repeated by his private secretary, Monsignor Rinaldo Angeli. Leo XIII truly saw, in a vision, demonic spirits who were congregating on the Eternal City (Rome). The prayer that he asked all the Church to recite was the fruit of that experience. He would recite that prayer with strong, powerful voice: we heard it many a time in the Vatican Basilica. Leo XIII also personally wrote an exorcism that is included in the Roman Ritual. He recommended that bishops and priests read these exorcisms often in their dioceses and parishes. He himself would recite them often throughout the day.”

The Prayer written by the Pope is of course the famous prayer to Saint Michael:

Sancte Michael Archangele,
defende nos in proelio;

contra nequitiam et insidias diaboli esto praesidium.

Imperet illi Deus, supplices deprecamur:

tuque, Princeps militiae Caelestis,

satanam aliosque spiritus malignos,

qui ad perditionem animarum pervagantur in mundo,

divina virtute in infernum detrude.
Amen.

This is the version I learned as a boy:

Saint Michael, the Archangel, defend us in the battle.

Be our protection against the malice and snares of the Devil.

We humbly beseech God to command him.

And do thou, O Prince of the Heavenly Host,

by the powers of God,

cast into Hell Satan and all the evil spirits

who prowl about the world seeking the ruin of souls.

http://the-american-catholic.com/2010/01/24/pope-leo-and-saint-michael-the-archangel/