8 Since, as We have said, public prayers are much more excellent and more efficacious than private ones, so ecclesiastical writers have given to the Rosary Sodality the title of "the army of prayer, enrolled by St. Dominic, under the banner of the Mother of God," - of her, whom sacred literature and the history of the Church salute as the conqueror of the Evil One and of all errors. The Rosary unites together all who join the Sodality in a common bond of paternal or military comradeship; so that a mighty host is thereby formed, duly marshalled and arrayed, to repel the assaults of the enemy, both from within and without. Wherefore may the members of this pious society take to themselves the words of St. Cyprian: "Our prayer is public and in common; and when we pray, we pray not for one, but for the whole people, for we, the entire people, are one" (De Orat. Domin.). The history of the Church bears testimony to the power and efficacy of this form of prayer, recording as it does the rout of the Turkish forces at the naval battle of Lepanto, and the victories gained over the same in the last century at Temesvar in Hungary and in the island of Corfu. Our predecessor, Gregory XIII, in order to perpetuate the memory of the first-named victory, established the feast of Our Lady of Victories, which later on Clement XI distinguished by the title of Rosary Sunday and commanded to be celebrated throughout the universal Church.
Source: Augustissimae Virginis Mariae (Vatican.va)