I think the beast upon whom the whore rides is Rome.
The idea of beast suggests a wild or untamed, undomesticated animal. The Greek word is closely related to the concept of hunting, particularly the idea of "game", or an animal that is hunted (as opposed to domesticated animals).
Such an idea lends itself symbolically to a people group who are outside the covenant of God, who are, in their wildness, "lawless", or practitioners of iniquity.
Such a people group would have to be outsiders or foreigners to the land of Israel, encroaching, then invading, then finally subduing it, such as occurred less than a hundred years after Rome defeated the Achaean League (Greece) at the Battle of Corinth in 146 B.C. (the same year Rome defeated Carthage). From that point forward, Israel lay open to Rome and was annexed after Pompey successfully besieged Jerusalem in 63 B.C. From then on, Israel was a vassal land to Rome and eventually came under the rule of the Herodian kings.
King Herod the Great, who died in 4 B.C. is the Herod who tried to have the Lord Jesus assassinated as a small boy.
This beast, as described in
Revelation 17, is the same beast mentioned in
Revelation 13 (the first of the two). We see this beast has incorporated into its body the vestiges of other, previous world empires (leopard, bear, lion), identifiers from Daniel's vision (
Daniel 7).
The second beast, from chapter 13, that looks like a lamb but speaks like a dragon, who has two two horns, is the false anointed one, that is, the High Priest (or the High Priesthood in general). In the OT, the High Priest, whether Aaron, or another, were called
Maschiach or Anointed One, just as Jesus would have been called by any speakers of Hebrew.
The sacred garments of the High Priest in those days were closely guarded by Rome in the Fortress Antonia (including the Umin and Thummim). Whether Annas and his five sons or Caiaphas, Annas' son in law, all held their post as High Priest at the whim of Rome and her representative, the Procurator (whether Pilate, or others before and after him).
When the Jewish rabble cried out to Pilate that if he released Jesus, he was no "friend of Caesar", it has to be understood that "Friend of Caesar" was an offical title appointed to certain members of the Roman aristocracy who merited such favor. (See
here. This charge was instigated by the High Priest who was trying to assert some level of dominance over his Roman masters, to threaten Pilate in order to curry favor with the Jews (who despised Pilate as a murderer), so they could claim to be the truer servants of Caesar.
The point of all this is to show how much Rome and Jerusalem were intertwined, connected, and "in bed" together, as the saying goes. But look what happens in
Revelation 17:16 through to chapter 18*. The beast (Rome), who hates the whore (Jerusalem), turns on her, and murders her (culminating in the destruction of the city in 70 AD).
[*In
Revelation 18:13, we are told that "Babylon" who had fallen, traded in, among other spices and incense, cinnamon. A little known truth is, at that time, and for centuries before then, cinnamon was only available from, chiefly, the island of Sri Lanka or Ceylon, by way of India. This spice, to find its way into the hands of the Roman elite (Nero burned a year's supply at his wife's funeral), would have to go through the Middle East, either by the sea southward under the Arabian peninsula into Egypt, or over land to the Mediterranean, meaning it made its way through Jerusalem. Note, then, too, how cinnamon was one of the ingredients in the sacred apothecary of the holy anointing oil, which was frequently made and used by the priests who ruled from the Temple. This helps to establish that Jerusalem is the city being referenced in
Revelation 18 as "Babylon". Therefore, as such, the only possible conclusion, if Jerusalem is MYSTERY BABYLON, the beast she rode was Rome.]