“To err knowingly is a sin: the ignorant are some times pardoned. You cannot deny that you know the Episcopal chair in the city of Rome was first bestowed on Peter: that Peter, the head of all the Apostles, sat therein; in which one chair unity should be preserved by all—so that now, whoever would place another chair against this one, would be guilty of schism.”  St Optatus, of Mela in Africa, addressing the Donatists  (S. Optatus Mil. l. ii. n. 2.)