Well if you look over to Revelation 17 it gives the answer to what it is speaking of there is chapter 13. But just like it is all symbolized in 13, the answers are also in symbolic language in 17. There are a few hints in 17 though and they indicates that this may be speaking from a future perspective, the first verse gives you the time frame.
Rev 17:1 Then one of the seven angels who had the seven bowls came and talked with me, saying to me, "Come, I will show you the judgment of the great harlot who sits on many waters,
It seems this was probably a vision of the future, because verse 3 says John was "carried me away in the Spirit into the wilderness." Also verse 8 indicated that it is speaking of the next age because the angel tells John, the beast that you saw was (the beast rules in this present age) and is not (it will not reign when Christ is ruling in the next age).
Rev 17:8 The beast that you saw was, and is not, and will ascend out of the bottomless pit and go to perdition. And those who dwell on the earth will marvel, whose names are not written in the Book of Life from the foundation of the world, when they see the beast that was, and is not, and yet is.
Reading that chapter from this perspective helps a lot to better understand what it's talking about. The seven heads - mountains - kings on the beast seems to be different eras of this world, throughout the ages as this chapter speaks of all ages of the beast. Verse 10 even speaks of the one (beast) that "has not yet come" that will return for "a little while" at the end of the next age (2nd witness Rev 20:3), "until the words of God are fulfilled" (v. 17).
Hope that's not too confusing, it's just my take on it anyway.
mercy, peace and love
Kat