With a false bishop appointed for themselves by heretics, they dare even to set sail and carry letters from schismatics and blasphemers to the Chair of Peter and to the principal church [at Rome], in which sacerdotal unity has its source" (Epistle to Cornelius [Bishop of Rome] 59:14 [A.D. 252]).
The Lord says to Peter: "I say to you," he says, "that you are Peter, and upon this rock I will build my Church" . . . On him he builds the Church, and to him he gives the command to feed the sheep John 21:17], and although he assigns a like power to all the apostles, yet he founded a single chair [cathedra], and he established by his own authority a source and an intrinsic reason for that unity. Indeed, the others were that also which Peter was [i.e., apostles], but a primacy is given to Peter, whereby it is made clear that there is but one Church and one chair. So too, all [the apostles] are shepherds, and the flock is shown to be one, fed by all the apostles in single-minded accord. If someone does not hold fast to this unity of Peter, can he imagine that he still holds the faith? If he [should] desert the chair of Peter upon whom the Church was built, can he still be confident that he is in the Church? (The Unity of the Catholic Church 4 [A.D. 251]).