other · 180 · Lyon
The full title is a Refutation and Overthrow of the Knowledge Falsely So Called, and its method is to set the systems out in detail on the theory that they cannot survive being stated clearly. The part that matters here is in the third book. Against the claim that the apostles taught a secret doctrine handed on privately, Irenaeus answers that if they had had secrets they would have entrusted them to the men they left in charge of the churches — and that those men, and their successors, are known by name in every see. He then lists the bishops of Rome from Linus to Eleutherus to prove it can be done. That list is the earliest one anyone has, and the argument behind it is the reason a succession is something a person can look up at all. Almost all of it survives only in a Latin translation and in Armenian; the Greek is lost except in quotation.
To describe the Valentinian systems accurately enough that describing them would be enough — and then to say what the church holds instead.
Five books, the fullest account of second-century Gnosticism anyone has, and the argument from succession that this whole dataset is an attempt to draw.