St. Michael appearing one day to Antonia d'Astonac, a most devout servant of God, told her that he wished to be honored by nine salutations corresponding to the nine Choirs of Angels, which should consist of one Our Father and three Hail Mary's in honor of each of the angelic choirs.

DECREE for the Angelic Rosary

It is a pious tradition that the Archangel Michael Prince of the Celestial Army, had declared to a devout woman who was in the habit of honoring him daily with acts of homage, that he would be grateful if a special manner of prayer could be introduced in his honor and that of all the other Celestial choirs. He, therefore, would concede many favors to his devotees in their social necessities, especially in the Catholic Church, of which he is perpetual protector.

It was said that these special prayers in honor of the Celestial Prince were practised with great ardour by a cloistered Carmelite nun in the monastery of Vetralla, who died in the odor of sanctity in 1751. Since this devotion was practised with great profit for souls, some religious of the aforesaid monastery, desiring to render those spiritual benefits common to all the faithful, humbly petitioned to Pope Pius X, to obtain for those who devoutly recited these prayers the following indulgences:

1. 7 years and as many as 40 days each time the Angelic rosary is recited.
2. 100 days whenever the rosary is carried on the person or whenever the medal with the image of the Holy angels is kissed.
3. Plenary indulgence once a month if the rosary is recited daily, prayer will be said for the exaltation of the Holy Church and the preservation of the Sovereign Pontiff.
4. Plenary indulgence by the same means enjoined on the following festivities : 
1) the apparition of St. Michael on May 8th, 
2) St. Michael's dedication on September 29th, 
3) Dedication of St. Gabriel on March 18th, 
4) Dedication of St. Raphael on October 24th, 
5) Dedication of holy guardian angels on October 2nd.