At the death of Theophilus in 412, Cyril (about 34 years old) was elected to succeed Theophilus as archbishop of Alexandria. The early years of his reign were marked by controversy and intrigue, as Cyril was directly or indirectly implicated in conflicts with schismatic Christians, the Jewish community, the imperial officers of the city, and most notoriously with the mob lynching of the pagan philosopher Hypatia.
One of Cyril’s great achievements in the first 15 years of his reign was the vast output of biblical commentaries on both the Old and New Testaments. Cyril was not only the strong and often aggressive leader of the Christian community; he was also a profound scholar and biblical commentator, and his production of biblical commentary is one of the greatest in the ancient church.
Cyril is best known, however, for his extended series of conflicts with Nestorius, which began in 428. Until his death in 444, Cyril was occupied largely with the repercussions of his collisions with Nestorius.
This conflict is the first installment of what are known as the fifth-century Christological controversies. At the heart of the conflict was the issue of how to speak about Christ as both human and divine and how to understand and describe the role of the Virgin Mary.
The focal point of the debate was whether or not the term Theotokos, meaning “God-bearer,” could rightly be applied to the Virgin Mary. But beneath this question lay the broader issue of the Incarnation of the Son of God.
Nestorius was concerned to distinguish clearly what is divine in Christ from what is human (and so rejected the term Theotokos), while Cyril was intent on securing the position that Christ is “one Son,” the eternal Word of God become man.
At the heart of the controversy between Cyril and Nestorius was not merely a political rivalry but a nest of theological issues and a conviction by each that the other party was denying something essential to the Christian account of salvation.
The conflict reached its climax in the summer of 431 through a complex set of events at the Council of Ephesus. The final outcome was the deposition of Nestorius and the approval of the council that upheld Mary as Theotokos.
Actual reconciliation between Cyril and those who supported Nestorius only occurred two years later in 433 with Cyril’s signing of the Formula of Reunion. It was a tenuous agreement that was ruptured soon after Cyril’s death and led to a new outbreak of controversy that eventually resulted in the Council of Chalcedon.
Cyril’s legacy as a man and as an archbishop is hotly debated. Some cast him as the evil villain of the controversy, others, as the resolute hero. Whatever view one takes, he is unquestionably the key theologian for defining the doctrine of Christ, and both the Greek Church and Latin Church revere him for his accomplishments.
Pope Leo XIII proclaimed him a Doctor of the Western Church on July 28, 1882. His feast day is celebrated in the Western Church on June 27, and in the Eastern Church on January 18.