- Nestorius was enthroned as the archbishop of Constantinople in April of the year 428. His main representative and colleague was Anastasius.
- The monks of Constantinople (who had the support of Basil [not Caesarea], bishop Proclus, and the lawyer Eusebius) came to Nestorius with a theological question they wanted to be settled. They asked him to publicly approve the application of the title "Theotokos" (Mother of God) for Mary. According to McGuckin, these monks were clashing against Anastasius, who denied the term Theotokos.
- At first, Nestorius tried to achieve some form of compromise by proposing the term "Christotokos" (Mother of Christ). This is because he viewed the term "Theotokos" as implying that Christ's divinity came directly from Mary. On the other hand, Nestorius disliked the term Anthropotokos because it could imply that Christ was merely a man.
- Rather than Nestorius' term "Christotokos" resolving what at once was a minor dispute, things began to get more and more heated. The monks began to accuse him of being like Paul of Samosata, who denied the deity of Christ altogether.
- According to McGuckin, St. Cyril was aware of the controversy with Nestorius and the monks of Constatinople from the very beginning through networks of monastic travel.
- In 429, Nestorius began giving public lectures in Constantinople on what he believed to be the proper christology. He openly attacked the Theotokos title.
- Bishop Proclus made a counter-attack against Nestorius when he preached a sermon on the Virgin Mother of God. There was a great applause for the sermon, which annoyed Nestorius.
- Copies of Nestorius' sermons were sent to St. Cyril.
- Nestorius' opponents accused him of denying the deity of Christ. The most charitable interpretation they could give of his teaching was that of two-person christology, the human nature of Christ being a distinct hypostasis from the Logos. Whether or not Nestorius actually taught this heretical idea is debatable. But in the early church, the implications of a doctrine or teaching were just as important as the actual statements being made. Such was the case with Nestorius and his theological adversaries.
- Many viewed Diodore of Tarsus as being the immediate influence of Nestorius' thinking; as a "proto-Nestorian", if you will.
- In 429, St. Cyril composed a Paschal Homily. Though there is no explicit mention of the Nestorian affair, Cyril does articulate the fact that Christ was one divine person. This shows that Cyril was aware of the developments which were taking place with Nestorius in Constantinople.
- Things began to get more heated when the lawyer Eusebius began posting a placard around the city which claimed that Nestorius was reigniting the heresies of Paul of Samosata. When Nestorius was preaching his sermons, there would be hecklers and disruptions in the audience.
- The monks made a formal petition to the Emperor requesting that Nestorius be tried for heresy.
- Finally, St. Cyril began to get publicly involved. He wrote a letter to the Monks of Egypt, arguing against Nestorius. Copies of it were sent to Constantinople.
- Nestorius commissioned Photius, one of his colleagues, to write up a response to the arguments made by St. Cyril. He also began to take political actions against his opponents. Specifically, he began to hear complaints of Alexandrian clerics, and of Western exiles, in an attempt to ruin the reputation of St. Cyril.
- Nestorius heard the complaints of clerics and lay people who claimed they had been unjustly treated by St. Cyril in Alexandria. Cyril later replied to the accusations against him in his 2nd letter to Nestorius.
- Throughout this, Nestorius was making appeals to Rome and to Pope Celestine. They were repeatedly ignored.
- Nestorius invited bishop Dorotheus of Marcianopolis to preach in the cathedral church. There, Dorotheus openly anathematized anyone who would call Mary the mother of God.
- Cyril, hearing of these proceedings, sent his famous 2nd letter to Nestorius. It ended up being a standard for orthodox christology at Ephesus and Chalcedon.
- In 430, Cyril wrote his Five Tomes Against Nestorius.
- Cyril dedicated a treatise to the emperor known as De Recta Fide, in which he presents one of his key arguments against Nestorius, namely that if it is not God who personally effects our salvation as the subject of our salvation, then salvation is ineffectual and pointless.
- On separate occasions, Cyril appealed to Theodosius and the royal women. However, it did not help his cause.
- This backfire on Cyril seems to have made Nestorius feel secure under the "protection of the emperor". At this time, Nestorius also wrote to John of Antioch requesting his help. John of Antioch urgued Nestorius to be cautionary in his approach to the dispute with Cyril and his other opponents.
- Nestorius petitioned the emperor to call a synod, presumably in order to put St. Cyril on trial.
- Nestorius wrote a letter to Pope Celestine in which he claims that the Theotokos dispute was Cyril’s way of avoiding his own trial and problems.
- The clergy of Constantinople drafted a petition to the Emperor, calling for Nestorius to be removed from his office. Cyril’s agents sent him a draft of this wanting his approval, but he rejected it, saying that he would not short-cut ecclesiastical law.
- In the summer of 430, Cyril’s Five Tomes Against Nestorius began to circulate and spread his views.
- Cyril wished the help of the Oriental Syrian churches, knowing that they were a “problematic area”. To do this, he wrote a letter to Acacius of Beroea. Acacius however replied by saying that he refused to be drawn into the dispute and controversy.
- Around this time, the Roman archdeacon Leo (later Pope Leo the Great) had been consulting with John Cassian in regards to the controversy with Nestorius. Cassian replied by pronouncing Nestorius as unorthodox and heretical, connecting him with Pelagianism.
- A synod was called at Rome on August 11, 430 where Nestorius was formally condemned by Pope Celestine and the other bishops who were present. The Roman synod communicated its verdict to Nestorius (who was given 10 days to renounce his views) and to the East, particularly John of Antioch, Juvenal of Jerusalem, Rufus of Thessalonica, and Flavian of Philippi.
- Cyril summoned his own synod of Egyptian bishops at Alexandria only a couple of months after the synod at Rome in August (mentioned above). There, Cyril made a formal exposition of orthodox christology in his 3rd letter to Nestorius and also produced the Twelve Chapters or Anathemas, against Nestorius. Cyril made acceptance of the anathemas as the condition for Nestorius to be readmitted into communion and the church.
- John of Antioch urged Nestorius to submit the verdict of the synod of Rome, as did many other Oriental bishops.
- Many accused Cyril of teaching the Apollinarian heresy. Cyril composed his Explanation of the Twelve Chapters, in defense against this false charge against him. From that point on, Theodoret of Cyrus and Andrew of Samosata were his main opponents within the Antiochene tradition.
- Nestorius received the verdict of his condemnation in the imperial city in the cathedral, during the liturgy. Four legates gave the relevant documents to Nestorius. He asked them to come back the next morning. But he was so angry that he refused any interview with them when they came back the next day.
- Nestorius preached a sermon where he viewed Cyril’s political ambitions as the real matter of controversy and conceded to accept the term “Theotokos”, for the sake of ending the dispute and schism. He then invited Cyril to come to the imperial city and have a civil discussion to settle the controversy.
- Theodosius then summoned the council at Ephesus, though Nestorius wanted it to be held at Constantinople. When the summons was sent out to all major Christian leaders, Nestorius and Cyril were both worried that things would not go their way. Nestorius sought to depict Cyril’s Twelve Anathemas as being a revival of the Apollinarian heresy. Theodoret and Andrew of Samosata made similar accusations against Cyril, both of them writing books against him.
- Cyril replied to the the Antiochene theologians (such as Theodoret) between December 430 and May 431, in two treatises, Response to the Orientals and To Euoptus (Against Theodoret). He repeatedly denied the accusation of Apollinarism. He defined Apollinarism (denying that Christ had a human mind or soul [Nous], and that Christ's human flesh was not of true human derivation) and then proceeded to refute it, and show that his earlier work was not teach this heresy.
- Cyril knew that Nestorius and the Antiochene theologians hadn't yet explicitly affirmed single-subject christology. So, he wrote to Pope Celestine in order to make sure that Nestorius appeared at the Council of Ephesus as the defendant, not as the accuser.
- Theodosius II set the council of Ephesus to open officially at Pentecost of 431 (June 7th). Count Candidian was to supervise the council (not as presiding over it; that position went to St. Cyril) and the city of Ephesus, keeping away lay people or monks who wanted to see what was going on for the sake of curiosity. He wanted to be sure that all of the bishops had the time to resolve this controversy entirely and definitively.
