Letter 177: The illustrious Aristolaus has sent a magistrianus [imperial courier] from Egypt with a letter from Cyril in which...

To Andreas, Bishop of Samosata, The illustrious Aristolaus has sent a magistrianus [imperial courier] from Egypt with a letter from Cyril in which he anathematizes Arius, Eunomius, and Apollinaris, and all who claim that Christ's Godhead is capable of suffering and who teach the confusion and blending of the two natures. At this we rejoice, though he did withhold his assent from our own statement. He further requires us to subscribe to the condemnation already passed, and to anathematize the teaching of the holy bishop Nestorius. Your holiness well knows that if anyone anathematizes, without qualification, the teaching of that most holy and venerable bishop, it is just the same as though he were anathematizing true religion itself. If we are compelled, then, we must anathematize those who call Christ a mere man, or who divide our one Lord Jesus Christ into two sons and deny His divinity -- and so on. [That is, we can condemn specific errors without condemning Nestorius himself.]

Letter 177