The Battle of Lepanto was a pivotal moment in the history of the Catholic Church.
A great concern of Pius V’s pontificate and one that occupied his final years was the encroachment of the Turks with their victory over the Venetians in Cyprus. This led to the high point of his foreign policy. He was able to form an alliance against the Turkish fleet at Lepanto, defeating them, thereby putting an end to their influence in the Mediterranean. The Battle of Lepanto took place in October of 1571. 30,000 Turks were killed, 10,000 were taken prisoner, 90 ships were sunk, 180 were captured, and 15,000 Christian slaves were set free.
Pius V attributed this victory to Mary and established a feast in her honor to commemorate it. Eventually it became the Feast of Our Lady of the Rosary, and the month of October became dedicated to her. In his Apostolic Constitution on Praying the Rosary, 1569, Pius outlined his great faith in Mary and his devotion to her through this prayer dedicated to her.