Sempiternus Rex Christus §4

⁴ Now, to treat of things in due order, let us recall from the beginning the events which we commemorate. The originator of the whole controversy under discussion at Chalcedon was Eutyches, a priest and archimandrite in a famous monastery of Constantinople. This man, in refuting the Nestorian heresy which maintained that there were two persons in Christ, fell into the opposite error.