This feast was established by Pope Pius V to commemorate the great victory of the Christian army against the Turks in the Battle of Lepanto in 1571.
All soldiers on the battlefield prayed the Rosary for three hours and the wind has shifted in their favor. They were able to defeat an army three times bigger, in one of the greatest naval victory in history.
Pope Pius V named this the Feast of Our Lady of Victories, to be celebrated on October 7th.
In 1573, Pope Gregory XIII changed the title of this memorial to Feast of the Holy Rosary.
Pope Paul VI established the form that we celebrate this feast today, in 1969 under the name “Our Lady of the Rosary”.
“The celebration of this day invites all to mediate upon the mysteries of Christ, following the example of the Blessed Virgin Mary who was so singularly associated with the incarnation, passion and glorious resurrection of the Son of God.”
Madonna del Rosario
Caravaggio
1607
1. Sign of the Cross: In the name of the Father, and of the Son, and of the Holy Spirit. Amen.
2. The Apostles Creed: I BELIEVE in God, the Father almighty, Creator of heaven and earth. I believe in Jesus Christ, His only Son, our Lord. He was conceived by the power of the Holy Spirit and born of the Virgin Mary. He suffered under Pontius Pilate, was crucified, died, and was buried. He descended to the dead. On the third day He rose again. He ascended into heaven and sits at the right hand of God, the Father Almighty. From thence He shall come to judge the living and the dead. I believe in the Holy Spirit, the holy catholic Church, the communion of saints, the forgiveness of sins, the resurrection of the body, and the life everlasting. Amen.
3. The Lord's Prayer: OUR Father, who art in heaven, hallowed be Thy name. Thy kingdom come. Thy will be done on earth as it is in heaven. Give us this day our daily bread and forgive us our trespasses as we forgive those who trespass against us. And lead us not into temptation, but deliver us from evil. Amen.
4. (3) Hail Mary: HAIL Mary, full of grace, the Lord is with thee. Blessed art thou amongst women and blessed is the fruit of thy womb, Jesus. Holy Mary, Mother of God, pray for us sinners, now, and in the hour of our death. Amen. (Three times)
5. Glory Be: GLORY be to the Father, and to the Son, and to the Holy Spirit. As it was in the beginning, is now, and will be forever. Amen.
Fatima Prayer: Oh, my Jesus, forgive us our sins, save us from the fires of hell, lead all souls to heaven, especially those in most need of your mercy.
Announce each mystery, then say 1 Our Father, 10 Hail Marys, 1 Glory Be and 1 Fatima prayer. Repeat the process with each mystery.
End with the Hail Holy Queen:
Hail, Holy Queen, Mother of Mercy, our life, our sweetness and our hope! To thee do we cry, poor banished children of Eve! To thee do we send up our sighs, mourning and weeping in this vale of tears! Turn then, most gracious advocate, thine eyes of mercy towards us; and after this, our exile, show unto us the blessed fruit of thy womb, Jesus!
O clement, O loving, O sweet Virgin Mary! Pray for us, O holy Mother of God, that we may be made worthy of the promises of Christ.
Final step -- The Sign of the Cross
The Mysteries of the Rosary
By tradition, Catholics meditate on these Mysteries during prayers of the Rosary.
The biblical references follow each of the Mysteries below.
The Joyful Mysteries
(Mondays and Saturdays)
1. The Annunciation (Luke 1:26-38) [Spiritual fruit - Humility]
2. The Visitation (Luke 1: 39-56) [Spiritual fruit - Love of Neighbor]
3. The Nativity (Luke 2:1-20) [Spiritual fruit - Poverty of Spirit]
4. The Presentation (Luke 2:21-38) [Spiritual fruit - Purity of mind & body]
5. The Finding of Jesus in the Temple (Luke 2:41-52) [Spiritual fruit - Obedience ]
The Luminous Mysteries or Mysteries of Light
(Thursdays) see Rosarium Virginis Mariae
1. Jesus' Baptism in the Jordan (II Corinthians 5:21, Matthew 3:17 and parallels) [Spiritual fruit - Gratitude for the gift of Faith]
2. Jesus' self-manifestation at the wedding of Cana (John 2:1- 12) [Spiritual fruit - Fidelity]
3. Jesus' proclamation of the Kingdom of God, with His call to conversion (Mark 1:15, Mark 2:3-13; Luke 7:47- 48, John 20:22-23) [Spiritual fruit - Desire for Holiness]
4. Jesus' Transfiguration (Luke 9:35 and parallels) [Spiritual fruit - Spiritual Courage]
5. Jesus' institution of the Eucharist, as the sacramental expression of the Paschal Mystery. (Luke 24:13-35 and parallels, 1 Corinthians 11:24-25) [Spiritual fruit - Love of our Eucharistic Lord]
The Sorrowful Mysteries
(Tuesdays and Fridays)
1. The Agony in the Garden (Matthew 26:36-46, Luke 22:39-46) [Spiritual fruit - God's will be done]
2. The Scourging at the Pillar (Matthew 27:26, Mark 15:15, John 19:1) [Spiritual fruit - Mortification of the senses]
3. The Crowning with Thorns (Matthew 27:27-30, Mark 15:16-20, John 19:2) [Spiritual fruit - Reign of Christ in our heart]
4. The Carrying of the Cross (Matthew 27:31-32, Mark 15:21, Luke 23:26-32, John 19:17) [Spiritual fruit - Patient bearing of trials]
5. The Crucifixion (Matthew 27:33-56, Mark 15:22-39, Luke 23:33-49, John 19:17-37) [Spiritual fruit - Pardoning of Injuries]
The Glorious Mysteries
(Wednesdays and Sundays)
1.The Resurrection (Matthew 28:1-8, Mark 16:1-18, Luke 24:1-12, John 20:1-29) [Spiritual fruit - Faith]
2. The Ascension (Mark 16:19-20, Luke 24:50-53, Acts 1:6-11) [Spiritual fruit - Christian Hope]
3. The Descent of the Holy Ghost (Acts 2:1-13) [Spiritual fruit - Gifts of the Holy Spirit]
4. The Assumption [Spiritual fruit - To Jesus through Mary]
5. The Coronation [Spiritual fruit - Grace of Final Perseverance]
This feast was instituted by Pope St. Pius V in thanksgiving for the great naval victory over the Turks at the battle of Lepanto on this day in the year 1570, a favor due to the recitation of the Rosary. This victory saved Europe from being overrun by the forces of Islam. 
Prominent among the clergy, Mark, the son of Priscus, was elected to the See of Rome just eighteen days after the death of St. Sylvester. A Roman, Mark was described as a man who was "filled with the love of God, the guardian of justice, a true friend of Christ."