The Marian Months of May and October
Why are the months of May and October dedicated to the Blessed Virgin Mary?
The Church has long set aside the entire month of May to honor Mary. According to this article, one reason was because in ancient Greece (remember, the Church went to Greece in its earliest apostolic missions) May was the month of Artemis, the goddess of fertility. Rededicating the month to the Mother of God was a way the early Christians sought to "baptize" pagan culture. As for October, that month has been dedicated to the rosary—a set of prayers said in honor of the Blessed Mother—because Pope St. Pius V credited the Holy League's victory at the Battle of Lepanto on October 7, 1571, to the praying of the rosary that he had enjoined upon all Christians in preparation for the battle.