After explaining the meaning of the beast, its seven heads and its ten horns (verses 8-12), and the meaning of the waters (verse 15), the angel now tells John explicitly that the prostitute is Rome, “the powerful city that rules over all kings of the world.” It may not be possible to speak of a city having power over kings, and so it may be necessary to say “the powerful city whose king rules over the kings of all nations in the world.”

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .