Revelations says that the whore sat on the beast and that the whore sat on seven hills. The seven hills characterize the beast, not the whore. The beast is the Roman Empire, but the whore is Jerusalem under Roman authority. St. John refers to Jerusalem as “the great city” and he refers to the whore as “the great city.” Therefore, it’s reasonable to conclude they are the same. Moreover, prostitution in the OT is always associated with Jerusalem or Israel, because only they were “married” to Yahweh and thus could go “whoring” after other gods. It seems unlikely that St. John would call a pagan city a “whore.” Finally, notice that the “whore of Babylon” is the counterpart of the New Jerusalem that comes down from heaven, which is the Bride of Christ. That’s because the whore is the old Jerusalem.