This prayer was said after mass at the foot of the altar. I heard that Pope Leo the X111 had a vision during mass of a terrific battle between st. michael and satan. He then called everyone to say this prayer he was the author. I was looking this up because I didn’t know where I heard it and saw that Pope Leo was the author. Pope John Paulxx111 also said we should continue to pray this prayer as Pope Leo visualized the battle noted in the apocolypse. It is very needed in our time. I also heard along with that that there was to be 100years of fierce battle from the time of Pope Leo.