That Christ Is One by Cyril of Alexandria (c. 376 - 444)

Cyril of Alexandria was the leading voice of Nicene orthodoxy in the Christological controversies between Constantinople (381) and Chalcedon (451). Assuming the mantle of the Cappadotian fathers, he answered the arguments of Nestorius who had changed the liturgy of Constantinople by altering the prayer which referred to Mary as the Mother of God. Although he died seven years before the Council of Chalcedon, his writings and formulations heavily influenced not only Chalcedon, but the entire trajectory of orthodox christological thought. (Summary by Jonathan Lange)