Cyril of Alexandria

Cyril of Alexandria (376 – 444) was Bishop of Alexandria in Egypt, and a leading theologian of the early Church. He helped protect against the Nestorian heresy which divided the person of Christ in two, and his work underpinned the conclusion of the Council of Chalcedon in 451.
Cyril's Second Letter to Nestorius is an attempt to correct false teaching. Cyril argues for the unity of the person of Christ, examining Christ's pre-existence, birth, suffering, and death.  
Cyril's third letter his colleague, Nestorius, is a more lengthly and robust argument against his false teaching. It includes twelve 'anathemas' (curses) which Cyril hoped Nestorius would accept.