Jeffro:
‘Babylon the Great’ was Rome.
peacefulpete:
The final redactor no doubt had contemporary Roman events in mind, but theunderlying texts were thoroughly Jewish and likely predate 70CE.
The initial chapters and much of the end times elements of Revelation were almost certainly from other Jewish works, some of which could predate 70, to which references to Roman opposition and imagined divine punishment were added. The parts about ‘beasts’ (alluding to various emperors and the empire itself) and references to time periods (in reference to the tribulation from 66-70) were necessarily later additions.
In its present form, ‘Babylon the Great’ unequivocally refers to Rome (at the time of writing). Whether there was some earlier work that referred to Jerusalem as ‘Babylon the Great’ is impossible to say, but the presentation in what we have as Revelation is not about Jerusalem.