(This was the first and to that time, the worst persecution of the Church in the First Century).
Thus, though Irenaeus gives us a lot of good biblical insight, he is less reliable for testimony referencing dates and time frames.
It is on him that most other Father’s based their conclusion.
But it must be said, that in terms of dating, Ireneus is a bit unreliable.
If the book was written in the final decade of the first century (the traditional view), then its prophecies probably do not concern the destruction of Jerusalem, an event that would have already taken place. As the word suggests, external evidence looks to material apart from and outside the book itself, such as the testimony of ancient writers or citations, quotes, or allusions from other writers, and so forth. Gentry canvasses other internal evidence for an early date of Revelation, such as the question of emperor worship, the role of Jewish Christianity, the looming Jewish war, and the role of Nero. Irenaeus's credibility is enhanced, not only by his important defense of the faith, but also by his claim to be a personal acquaintance of Polycarp, who in turn had known the Apostle John himself.
On the other hand, if Revelation was written before A. 70, then a case could be made that it describes chiefly those events leading up to Jerusalem's fall. "My confident conviction," concludes Gentry, "is that a solid case for a Neronic date for Revelation can be set forth from the available evidences, both internal and external. Irenaeous referred to Revelation in a work he wrote near the end of the second century, probably between A. Irenaeus's testimony regarding Revelation is found in book 5 of his famous work Against Heresies.
The five kings who have fallen would be Nero, Galba, Otho, Vitellius, and Vespasian.