John saw a vision of a Beast with seven heads.

These 'heads' or 'mountains' or 'empires' are described as seven successive kings.

Five of these 'kings' had already fallen in John's day; Egyptian, Assyrian, Babylonian, Medo=Persian and Grecian empires.

An angel told him that one world empire remained and that was number six. It was the great Roman Empire which existed in John's time.