Revelation 17:9 - Matthew Poole's English Annotations on the Holy Bible

And here is the mind which hath wisdom; that is, here is that which requireth a mind endued with spiritual wisdom. The seven heads are seven mountains, on which the woman sitteth; the seven heads which he saw the beast with, signified seven mountains or hills upon which Rome is situated; they were named before: See Poole on "Revelation 17:3". They tell us now Rome is situated in Campo Martio. Resp. Whatever it now is, certain it is, that in St. John's time it was situated upon them, and they are now within the compass of Rome.