Ad Caeli Reginam
Ad Caeli Reginam is an encyclical of Pope Pius XII, given at Rome, from St. Peter's, on the feast of the Maternity of the Blessed Virgin Mary, the eleventh day of October, 1954, in the sixteenth year of his Pontificate. The encyclical is an important element of the Mariology of Pope Pius XII. It established the feast Queenship of Mary.
The title "Queen of Heaven" is given to Mary based primarily on her role as Mother of Jesus Christ. It is found in the liturgy of the hours (Hail, Holy Queen...) and popular piety (Litany of Loreto). The title of "Queen" is frequently found in Benedictine monasticism. Its use underwent a notable development in the Cistercian reform movement and in the orders of evangelical--apostolic life that arose from the beginning of the twelfth century onwards. Over time this title of Mary became generally accepted so that with the encyclical Ad Caeli Reginam, of October 11, 1954, Pope Pius XII instituted the feast of the Queenship of Mary.
Mary should be called Queen, not only because of her Divine Motherhood of Jesus Christ, her only son, but also because God has willed her to have an exceptional role in the work of salvation. The encyclical argues that because Christ is the Redeemer, he is Lord and king by a special title, so too, the Blessed Virgin also is queen, by virtue of the unique manner in which she assisted in the redemption.
Mary was chosen as Mother of Christ in order that she might become a partner in the redemption of the human race: "As Christ, the new Adam must be called a King not merely because He is Son of God, but also because He is our Redeemer, so, analogously, the Most Blessed Virgin is queen not only because she is Mother of God, but also because, as the new Eve, she was associated with the new Adam."
The Church has always taught that Mary is far above all other creatures in dignity, and after her Son possesses primacy over all. "You have surpassed every creature," sings St. Sophronius. "What can be more sublime than your joy, O Virgin Mother? What more noble than this grace, which you alone have received from God"? To this St. Germanus adds: "Your honor and dignity surpass the whole of creation; your greatness places you above the angels." And St. John Damascene goes so far as to say: "Limitless is the difference between God's servants and His Mother." 
Pius XII quotes his predecessors: Pope Pius IX, "With a heart that is truly a mother's," does she approach the problem of our salvation, and is solicitous for the whole human race; made Queen of heaven and earth by the Lord, exalted above all choirs of angels and saints, and standing at the right hand of her only Son, Jesus Christ our Lord, she intercedes powerfully for us with a mother's prayers, obtains what she seeks, and cannot be refused." Leo XIII, said that an "almost immeasurable" power has been given Mary in the distribution of graces; St. Pius X adds that she fills this office "as by the right of a mother."  Pius XII admonishes theologians and preachers from straying from the correct course, avoiding two extremes, Marian exaggerations and excessive narrowness of mind.
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The encyclicals points to some countries of the world, where people are unjustly persecuted for their Christian faith and who are deprived of their divine and human rights to freedom. Reasonable demands and repeated protests have not helped them. “May the powerful Queen of creation, whose radiant glance banishes storms and tempests and brings back cloudless skies, look upon these her innocent and tormented children with eyes of mercy” 
- From the earliest ages of the catholic church a Christian people, whether in time of triumph or more especially in time of crisis, has addressed prayers of petition and hymns of praise and veneration to the Queen of Heaven. And never has that hope wavered which they placed in the Mother of the Divine King, Jesus Christ; nor has that faith ever failed by which we are taught that Mary, the Virgin Mother of God, reigns with a mother's solicitude over the entire world, just as she is crowned in heavenly blessedness with the glory of a Queen.
- Pope Pius XII, Mariological encyclicals and bulls:
- Acta Apostolicae Sedis. (AAS), Vatican City 1939-1958. Official documents of the Pontificate of Pope Pius XII
- Servants of the Magnificat: The Canticle of the Blessed Virgin and Consecrated Life, Order of Servants of Mary, 1996
- "Why do we call Mary Queen?", The Marian Library, University of Dayton
- Pope Pius XII, Ad Caeli Reginam §38, October 11, 1954, Vatican
- Ad caeli regnam §40
- Ad caeli reginam §42
- Ad caeli reginam §44
- Ad caeli reginam §50
- Ad caeli reginam §1