St. Cyril was born in Alexandria, Egypt, in 370 AD. His family was of the noble class. His uncle was Patriarch Theophilus of Alexandria. Cyril received a classical and theological education under his uncle, who eventually ordained him to the priesthood. A number of years later, in 412 AD, he succeeded his uncle as the patriarch or bishop of Alexandria.
Cyril was a fierce advocate for orthodox teaching and he aggressively went on the offensive against those who taught otherwise. He strenuously opposed three major heresies that had numerous adherents in the Fifth Century: Novatianism, which argued that certain sins such as murder, adultery, and apostasy, could not be forgiven by the sacraments; Nestorianism, which held that Jesus has two separate persons, one human, the other divine, and that Mary was the mother only of the human person; and Pelagianism, which held that salvation is achieved only through human effort and not by grace. With decisiveness and stern authority, he closed the churches of heretical sects and expelled the Jews from Alexandria.
While Cyril’s actions provoked intense anger and bitter opposition, he was supported by Pope Zosimus (417-418) and a large number of bishops.
Meanwhile, Nestorius became the patriarch of Constantinople in 428, and he held that Jesus was the greatest of human beings but not divine, and that Mary was not the mother of God. Cyril vehemently opposed Nestorius and his teaching, and he brought the matter to the attention of the new pope, Celestine I (422-432), who convoked a synod in Rome that condemned Nestorianism. A decree was issued that condemned the teachings of Nestorius and removed him as patriarch, but Nestorius rejected the synod’s decision.
With the church beset by controversy, the Roman Emperor, Theodosius I, called for a council to resolve the conflict for the sake of peace in the empire. The Council of Ephesus was convened in 431, Cyril presided, and two hundred bishops attended. In a tactical move, the sessions began before forty-three oriental bishops that supported Nestorius arrived. Under the leadership of Cyril, the council upheld the two natures of Jesus, proclaimed Mary as the Mother of God, and condemned Nestorianism.
When Archbishop John of Antioch and the other bishops that supported Nestorius arrived, they were outraged, convened a counter council, denounced Cyril as a heretic, and deposed him. Aggravated by the dispute, Emperor Theodosius arrested and imprisoned both Cyril and Nestorius. Pope Celestine issued a proclamation in support of Cyril and the Council of Ephesus, and when papal legates arrived, Cyril was exonerated and released, while the charges against Nestorius were confirmed and awhile later was exiled.
After the Council of Ephesus, Cyril dedicated himself to writing a number of treatises to explain the doctrine of the Trinity, the mystery of the Incarnation, and the role of the Blessed Virgin Mary as the Mother of God. He also wrote Scripture commentaries on the Pentateuch and the gospels of Luke and John, and he supported the Egyptian monasticism. Cyril died in 444 in Alexandria, and he was declared a Doctor of the Church by Pope Leo XIII in 1882.