The dating of revelation
There are basically two conservative views as to when the book of Revelation was written: (1) it was written in the late-90s AD, toward the end of Domitian’s reign; or (2) it was written sometime prior to 70 AD, during the reign of Nero.
So why does Eusebius appeal to this statement from Irenaeus? It seems to me that the only way for the Irenaeus quote to count as “ample evidence” for John’s exile to Patmos under Domitian is if Eusebius were assuming two things: (1) that ἑωράθη (“it was seen”) refers to the apocalyptic vision itself, rather than to John himself, contrary to what I argued above; and (2) that the testimony of Revelation 1:9 is authentic: “I, John, your brother and partner in the tribulation and the kingdom and the patient endurance that are in Jesus, was on the island called Patmos on account of the word of God and the testimony of Jesus.” In other words, Eusebius would be reasoning as follows: 1.
You could argue that both statements are sensible enough, but I think the first one makes better sense. In making this decision, we also need to consider other things Irenaeus says about the book of Revelation.
In fact, very shortly before the oft-referenced quote above, Irenaeus states that the number 666 is “found in all the most approved and ancient copies” of Revelation (Against Heresies, 5.30.1). Irenaeus makes reference to “ancient copies” of the book of Revelation. they had been around a very long time), but they were also in fact copies (i.e. So when Irenaeus, just a couple paragraphs later, speaks of something that “was seen not a long time back, but almost in my own lifetime,” how could that be a reference to the vision of Revelation?
So bear in mind that when Eusebius produces this quote from Irenaeus, he’s not doing so in order to make a point about the date of Revelation.
He’s only trying to make a point about John himself.