|The number of the beast is 666 by William Blake.|
|Fragment from Papyrus 115 (P115) of Revelation in the 66th vol. of the Oxyrhynchus series (P. Oxy. 4499). has the number of the beast as χιϛ, 616.|
This was achieved through Gematria:
"...transforming names into numbers (gematria) was common in antiquity. For example, in the Lives of the Twelve Caesars Roman historian Suetonius identifies Nero by a numerical designation equal to a nefarious deed. This numerical equality (isopsephism) is encapsulated in the phrase: “Count the numerical values of the letters in Nero’s name, and in ‘murdered his own mother’ and you will find their sum is the same.” In Greek the numerical value of the letters in Nero’s name (Greek: Nevrwn, English transliteration: Neron) totaled 1,005, as did the numbers in the phrase murdered his own mother. This ancient numerical cryptogram reflected the widespread knowledge that Nero had killed his own mother.
|Isopsephy from the Sanctuary of Artemis Orthia, 2nd century CE|
This method is not exclusively Jewish:
"In Greek isopsephy and Hebrew gematria, every letter has a corresponding numeric value. Summing these numbers gives a numeric value to a word or name. The use of isopsephy to calculate "the number of the beast" is used in many of the below interpretations."
The historical record for the reign of Nero mentions Chrestians, rather than Christians. Members of the Greco-Roman cult of Chrestianity came to oppose Nero, who was - according to the Emperor Domitian - assassinated by Epaphroditus. (Chrestianity of the First Century)
None of this means that Revelation was written in this time, because through the works of Josephus and others, later authors had knowledge of both Nero and the first century; though it could well have been written towards the end of that century - the time of Domitian - a later date is very possible.