The Rosary developed gradually over many centuries. The practice of praying 150 Hail Marys (mirroring the 150 Psalms) emerged in medieval monasteries as a devotion for illiterate lay people who could not read the Psalter. According to tradition, the Blessed Virgin Mary appeared to St. Dominic in the 13th century and gave him the Rosary as a spiritual weapon against the Albigensian heresy, though modern historians debate this account. The Dominican Order was instrumental in promoting the devotion. By the 15th century, the practice of meditating on mysteries of Christ's life while praying Hail Marys became standardized. Pope Pius V officially established the feast of Our Lady of the Rosary in 1571 after the Christian victory at the Battle of Lepanto, which he attributed to the Rosary. Pope John Paul II added the Luminous Mysteries in 2002, expanding the traditional three sets (Joyful, Sorrowful, Glorious) to four. The Rosary remains one of the most beloved Catholic devotions worldwide.