Supremi Apostolatus Officio §3

³ This devotion, so great and so confident, to the august Queen of Heaven, has never shone forth with such brilliancy as when the militant Church of God has seemed to be endangered by the violence of heresy spread abroad, or by an intolerable moral corruption, or by the attacks of powerful enemies. Ancient and modern history and the more sacred annals of the Church bear witness to public and private supplications addressed to the Mother of God, to the help she has granted in return, and to the peace and tranquillity which she had obtained from God. Hence her illustrious titles of helper, consoler, mighty in war, victorious, and peace-giver. And amongst these is specially to be commemorated that familiar title derived from the Rosary by which the signal benefits she has gained for the whole of Christendom have been solemnly perpetuated. There is none among you, venerable brethren, who will not remember how great trouble and grief God's Holy Church suffered from the Albigensian heretics, who sprung from the sect of the later Manicheans, and who filled the South of France and other portions of the Latin world with their pernicious errors, and carrying everywhere the terror of their arms, strove far and wide to rule by massacre and ruin. Our merciful God, as you know, raised up against these most direful enemies a most holy man, the illustrious parent and founder of the Dominican Order. Great in the integrity of his doctrine, in his example of virtue, and by his apostolic labours, he proceeded undauntedly to attack the enemies of the Catholic Church, not by force of arms; but trusting wholly to that devotion which he was the first to institute under the name of the Holy Rosary, which was disseminated through the length and breadth of the earth by him and his pupils. Guided, in fact, by divine inspiration and grace, he foresaw that this devotion, like a most powerful warlike weapon, would be the means of putting the enemy to flight, and of confounding their audacity and mad impiety. Such was indeed its result. Thanks to this new method of prayer-when adopted and properly carried out as instituted by the Holy Father St. Dominic-piety, faith, and union began to return, and the projects and devices of the heretics to fall to pieces. Many wanderers also returned to the way of salvation, and the wrath of the impious was restrained by the arms of those Catholics who had determined to repel their violence.