There certainly are many different explanations of what the number 666 means in the book of Revelation. So why should anyone believe that it means Nero Caesar, as I argue in this post, rather than something else? There’s actually an intriguing bit of historical evidence that the earliest readers of the book understood it the way I’ve suggested.
The question of the meaning of the number 666 arose from a comment on a post I wrote about secret codes in the Bible. This number represents a name and it comes from gematria, the practice in languages that use letters for numbers of adding up the total value of the letters in a word. Gematria is something like a code, but there’s an important difference.
As a rule, if you know how a code works, you can decipher anything written in that code. But in gematria, you need to know the likely subject of the code in order to imagine possible solutions and test their numerical totals.
It appears that early followers of Jesus understood the number of the beast in Revelation to indicate Nero Caesar (that is, to point to the imminent resumption of imperial persecution) because at least one early copyist seems to have known that this was the solution to the code, but couldn’t get the numbers to add up, and so wrote 616 instead, a number the copyist thought did work!
Here’s what likely happened. As Bruce Metzger suggests in his Textual Commentary on the New Testament, “Perhaps the change was intentional, seeing that the Greek form Neron Caesar written in Hebrew characters is equivalent to 666, while the Latin form Nero Caesar is equivalent to 616.” (The difference is the Hebrew letter Nun, which has a value of 50.) Whatever copyist first introduced the change was thinking of Nero’s name in Latin rather than Greek, and so wrote in 616.
We don’t know when this variant reading first appeared, but it was quite early, since Irenaeus discusses it in Against Heresies, which he wrote around AD 180. He notes that 666, not 616, is the number “found in all the most approved and ancient copies” of the book of Revelation, and that “those men who saw John face to face” attest to it. So 616 was recognized early on as a change. But that’s the whole point: it’s a change that was made so early it was likely introduced by someone who knew what Revelation wanted to say and who was trying to get the numbers to add up.

The change in the text was copied into later manuscripts. The first written evidence we have of this reading is in an Egyptian papyrus fragment that dates to about AD 225-275. The reading 616 also appears in Codex Ephraemi Rescriptus, compiled about 200 years later, which is one of the four major uncial manuscripts that are key resources for New Testament textual criticism.
This variant reading provides a vital clue that the interpretation of 666 as gematria for Nero(n) Caesar is correct. The implications are, as I say in my Daniel-Revelation study guide, that the meaning of this number “has a unique solution based on the conventions of apocalypses and the facts of history. Its main purpose is to delegitimize Domitian’s claims to divinity and to strengthen followers of Jesus who are being pressured by the emperor cult.” The take-home message for us today is that we should be equally faithful in resisting anything that rivals our loyalty to Jesus. But “the number 666 isn’t a coded biblical prediction of some invisible, demonic means of social control in the end times.”