In Revelation, in respect to the politcal wild Beast with seven heads and ten horns, these heads represent world powers and John said, at the time of his writing, five had been, one was (the Roman Empire) and one was yet to come and that that one would wage war with God at Armageddon. In his vision, the seventh head (the empire that was yet to come from John's perspective) is isolated and portrayed in more detail in the form of a solo wild Beast , the famous Beast that has the mark 666. Horns represent political empires and this solo Beast is portrayed as having two horns. It can't be the Roman empire because John wrote that it was yet to come!
I've tried to be brief and to the point but really this subject could be dealt with in an entire book. Hope this goes some way to clarifying your question!