St. Cyril of Alexandria (376 — 444 AD) was the Pope of Alexandria, from years 412 to 444 AD. Known as being the key figure against Nestorianism at the First Council of Ephesus, Cyril and his Christological teachings (Miaphysitism) have shaped the Church to what we know it to be, today!

Writings of St. Cyril of Alexandria:

First Letter of Cyril to Succensus

Second Letter of Cyril to Succensus