Cyril of Alexandria

Cyril of Alexandria (c. 376–444) was a Christian theologian and patriarch who defended Mary’s title Theotokos and opposed Nestorius in disputes over Christ’s unity.

Nestorius: Nestorius was a fifth-century archbishop of Constantinople whose teachings about Christ and Mary prompted a major church controversy. Cyril condemned Nestorius’s Christology and challenged his rejection of Theotokos.
Theotokos: Theotokos is a Greek title meaning “God-bearer,” used for Mary to affirm that the one she bore is God incarnate. Cyril defended the title as a consequence of Christ’s personal unity.
Council of Ephesus: The Council of Ephesus was an ecumenical council held in 431 that condemned Nestorius and affirmed Mary as Theotokos. Cyril presided over its opening proceedings and secured Nestorius’s condemnation.
Formula of Reunion: The Formula of Reunion was a 433 agreement between Cyril and John of Antioch that reconciled their churches after Ephesus. It shows how Cyril accepted a negotiated statement while retaining his core account of Christ.
Second Letter of Cyril to Nestorius: The Second Letter of Cyril to Nestorius is a theological letter explaining the unity of Christ and Mary’s title Theotokos. It states Cyril’s central position before the council’s formal proceedings.
Celestine I: Celestine I was bishop of Rome from 422 to 432 and supported Cyril against Nestorius. Cyril secured Celestine’s backing before the Council of Ephesus.
Hypostatic union: The hypostatic union is the doctrine that Christ’s divine and human natures are united in one person. Cyril argued that the Word united humanity to himself without ceasing to be divine.
Nestorianism: Nestorianism is a label for teachings seen as dividing Christ’s divine and human realities too sharply. Cyril accused Nestorius’s teaching of dividing Christ, though the label oversimplifies their disagreement.
Council of Chalcedon: The Council of Chalcedon was an ecumenical council held in 451 that defined Christ as one person in two natures. Its formula addressed disputes that continued after Cyril’s death and drew on his legacy.
Third Letter of Cyril to Nestorius: The Third Letter of Cyril to Nestorius is a letter demanding Nestorius accept Cyril’s Christological teaching and its accompanying anathemas. It became the document against which Nestorius was required to declare agreement.

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