Taken from The Secret of the Rosary by St. Louis de Montfort
Since the Holy Rosary is composed, principally and in substance, of the Prayer of Christ and the Angelic Salutation, that is, the Our Father and the Hail Mary, it was without doubt the first prayer and the first devotion of the faithful and has been in use all through the centuries, from the time of the apostles and disciples down to the present.
But it was only in the year 1214, however, that Holy Mother Church received the Rosary in its present form and according to the method we use today. It was given to the Church by Saint Dominic who had received it from the Blessed Virgin as a powerful means of converting the Albigensians and other sinners.
I will tell you the story of how he received it, which is found in the very well-known book "De Dignitate Psalterii" by Blessed Alan de la Roche. (1) Saint Dominic, seeing that the gravity of people’s sins was hindering the conversion of the Albigensians, withdrew into a forest near Toulouse where he prayed unceasingly for three days and three nights. During this time he did nothing but weep and do harsh penances in order to appease the anger of Almighty God. He used his discipline so much that his body was lacerated, and finally he fell into a coma.
At this point Our Lady appeared to him, accompanied by three angels, and she said:
"Dear Dominic, do you know which weapon the Blessed Trinity wants to use to reform the world?"
"Oh, my Lady," answered Saint Dominic, "you know far better than I do because next to your Son Jesus Christ you have always been the chief instrument of our salvation."
Then Our Lady replied:
"I want you to know that, in this kind of warfare, the battering ram has always been the Angelic Psalter which is the foundation stone of the New Testament. Therefore if you want to reach these hardened souls and win them over to God, preach my Psalter."
So he arose, comforted, and burning with zeal for the conversion of the people in that district he made straight for the Cathedral. At once unseen angels rang the bells to gather the people together and Saint Dominic began to preach.
At the very beginning of his sermon an appalling storm broke out, the earth shook, the sun was darkened, and there was so much thunder and lightning that all were very much afraid. Even greater was their fear when looking at a picture of Our Lady exposed in a prominent place they saw her raise her arms to heaven three times to call down God’s vengeance upon them if they failed to be converted, to amend their lives, and seek the protection of the Holy Mother of God.
God wished, by means of these supernatural phenomena, to spread the new devotion of the Holy Rosary and to make it more widely known.
At last, at the prayer of Saint Dominic, the storm came to an end, and he went on preaching. So fervently and compellingly did he explain the importance and value of the Holy Rosary that almost all the people of Toulouse embraced it and renounced their false beliefs. In a very short time a great improvement was seen in the town; people began leading Christian lives and gave up their former bad habits.
This miraculous way in which the devotion to the Holy Rosary was established is something of a parallel to the way in which Almighty God gave His law to the world on Mount Sinai and obviously proves its value and importance.
Inspired by the Holy Spirit, instructed by the Blessed Virgin as well as by his own experience, Saint Dominic preached the Holy Rosary for the rest of his life. He preached it by his example as well as by his sermons, in cities and in country places, to people of high station and low, before scholars and the uneducated, to Catholics and to heretics.