[Written a.d. 251. Although, in order of time, this treatise would be the third, I have placed it here because of its dignity, and because of its importance as a key to the entire writings of Cyprian; for this theory is everywhere the underlying principle of his conduct and of his correspondence. It illustrates the epistles of Ignatius as well as his own, and gives the sense in which the primitive Christians understood these words of the Creed, “the Holy Catholic Church.” This treatise has been subjected to falsifying interpolations, long since exposed and detected, to make it less subversive of the countertheory of Rome as developed by the school doctors. Elucidation I.]