Throughout history numerous Roman Catholic saints have attested to the central role of Mary in God's plan of salvation and have contributed to the growth of Mariology. This article reviews the Mariology of the saints, as a force that has shaped and transformed our current understanding of Marian dogmas, doctrines and devotions.
Beyond the teachings of the early Church Fathers, the growth of Mariology over the centuries has taken a somewhat unique path among other areas of theology in that it has been shaped by the interplay of three separate forces:
In many cases, the Mariological views of the Holy See have been gradually affected by sensus fidei which itself has been shaped by the writings of numerous saints throughout history who have attested to the central role of Mary in God's plan of salvation. Thus the saints have often acted as the force that drives sensus fidei which then affects Catholic teachings.
An example of this effect is the case of Saint Louis de Montfort. During his priesthood of only 16 years, he was mostly a missionary preacher who travelled from village to village on foot to deliver sermons, often risking everything along the way. His heated style of preaching and views were often the subject of serious criticism during his life. He was persecuted by the Holy Office, poisoned by critical locals and when he died in 1716 at age 43, each of the three congregations he left behind had but a handful of followers. When Blessed Marie Louise Trichet decided to join his order Daughters of Wisdom in 1700, her mother reportedly told her: "You will become as mad as that priest". Yet, over the centuries, de Montfort's Marian books such as True Devotion to Mary and Secret of the Rosary gathered a strong following among Catholics and in time influenced millions of people. The growth of his popularity and the spread of his approach of "total consecration to the Virgin Mary" was not driven from Rome but from the ground up as sensus fidelium gathered momentum in his favor. He was eventually declared a saint in 1947.
In recent years, one young seminarian who was affected by one of de Montfort's books said that he had "read and reread many times and with great spiritual profit" a work of de Montfort and it "had been a decisive turning point in his life". That young seminarian eventually became Pope John Paul II, based his personal motto "Totus Tuus" on de Montfort's influence, beatified Marie Louise Trichet and made a papal visit to pray on the tombs of Saint Louis and Blessed Marie Louise Trichet. Saint Louis is now a candidate to become a Doctor of the Church and his founders statue was recently placed in Saint Peter's Basilica at the Vatican.
Saint Irenaeus of Lyons (circa 140-202) is perhaps the earliest of the Church Fathers to develop a thorough Mariology. In his youth he had met Polycarp and other Christians who had been in direct contact with the Apostles. Irenaeus sets out a forthright account of Mary's role in the economy of salvation.
According to Irenaeus, Christ, being born out of the Virgin Mary, created a totally new historical situation.  This view influences later Ambrose of Milan and Tertullian, who wrote about the virgin birth of the Mother of God. The donor of a new birth had to be born in a totally new way. The new birth being that what was lost through a woman, is now saved by a woman. 
Saint Ambrose of Milan (339-397) is an early Church Father whose powerful Mariology influenced contemporary Popes like Pope Damasus and Siricius and later, Pope Leo the Great. His student Augustine and the Council of Ephesus were equally under his influence. Central to Ambrose is the virginity of Mary and her role as Mother of God.
Saint Augustine (354-430) did not develop an independent Mariology, but his statements on Mary surpass in number and depths those of other early writers.  The Virgin Mary “conceived as virgin, gave birth as virgin and stayed virgin forever  Even before the Council of Ephesus, he defended the ever Virgin Mary as the mother of God, who, because of her virginity, is full of grace  She was free of any temporal sin,  Because of a woman, the whole human race was saved. 
The Patriarch Cyril of Alexandria (412-444) became famous in Church history, because of his spirited fight for the title “Mother of God” during the Council of Ephesus (431). His writings include the homily given in Ephesus and several other sermons. . Some of his alleged homilies are in dispute as to his authorship. In several writings, Cyril focuses on the love of Jesus to his mother. On the Cross, he overcomes his pain and thinks of his mother. At the Marriage at Cana, he bows to her wishes. The overwhelming merit of Cyril of Alexandria is the cementation of the centre of dogmatic Mariology for all times. He created the basis for all other Mariological developments through his teaching of the blessed Virgin Mary, as the Mother of God.
Many early mariological concepts developed in the Eastern Church. From the West, Pope Damasus I and others defended Mary against Monophysitism, the teaching that Christ had only a divine nature. Accordingly, Mary is only the Mother of God, not the mother of the human Jesus. The most significant papal teaching opposing this view begin with Pope Martin I and continue with Pope Leo the Great. To define this issue, an ecumenical council was convoked first at Nicaea but later transferred to Chalcedon in the year 451. Leo the Great defended the teaching that Christ has two natures, one divine and one human.
To Leo the Great, Mariology is determined by Christology. If Christ would be divine only, everything on him would be divine. His eating would be symbolism. Only his divinity would have been crucified, buried and resurrected. Mary would only be the mother of God, and Christians would have no hope for their own resurrection. The nucleus of Christianity would be destroyed. He asks for the veneration of the Virgin Mary both at the manger and at the throne of the heavenly father. The most unusual beginning of a truly human life through her was to give birth to Jesus, the Lord and Son of King David.
In his encyclical Doctor Mellifluus on Bernard of Clairvaux, Pope Pius XII quotes three central elements of Bernard’s Mariology: How he explained the virginity of Mary, the “Star of the Sea", how the faithful should pray on the Virgin Mary, and, how Bernard relied on the Virgin Mary as Mediatrix.
Theologically, Bernard, a Doctor of the Church, is a fervent supporter of the Mediatrix interpretation of Mary. God and World meet in her.  Divine life flows through her to the whole creation. She is one with Jesus, who wants to save all and who passes all graces through her.  She is the mediatrix to god, the ladder on which sinners may climb up to him, the royal road to him, because she is full of grace
Alphonsus Liguori (1696.-1787) a Doctor of the Church, wrote the The Glories of Mary, Marian Devotions, Prayers to the Divine Mother, Spiritual Songs, Visitations to the Blessed Sacrament and to the Virgin Mary, The True Spouse of Jesus Christ, and other writings. He was of great influence on Mariology during the Age of Enlightenment. His often flaming Marian enthusiasm contrasts with the cold rationalism of the Enlightenment. Mainly pastoral in nature, his Mariology rediscovers, integrates and defends the Mariology of Augustine and Ambrose and other fathers and represents an intellectual defence of Mariology in the eighteenth century. 
Saint Louis de Montfort, was an effective defender of Mariology against Jansenism whose "True Devotion to Mary" synthesizes many of the earlier saints' writings and teachings on Mary. Saint Louis de Montfort's approach of "total consecration to Jesus Christ through Mary" had a strong impact on Marian devotion both in popular piety and in the spirituality of religious orders. One of his well known followers was Pope John Paul II. According to his Apostolic Letter Rosarium Virginis Mariae, the pontiff's personal motto "Totus Tuus" was inspired by St. Louis' doctrine on the excellence of Marian devotion and total consecration, which he quoted:
In an address to the Montfortian Fathers, the pontiff also said that his reading the saint's work The True Devotion to Mary was a "decisive turning point" in his life.
Saint Louis de Montfort impacted Mariology not only at the papal level, but the popular level. His book The Secret of the Rosary (which is a multi-perspective approach to the rosary) has been widely read by Catholics worldwide for over two centuries and is one of the earliest works to strengthen the devotional components of modern Mariology.