Revelation 17:10

And there are seven kings; the seven heads signify also seven kings. This is understood by many as representing the seven forms of civil government which prevailed in Rome-kings, consuls, dictators, decemvirs, military tribunes, emperors, and the exarchate of Ravenna; for here, as in verse Revelation 17:12, a king denotes not an individual, but a succession of rulers.

Five are fallen; the first five of the above list; which are those enumerated by the historian Livy, as having existed in his day.

One is; the imperial form.

When he cometh; when the last king cometh, that is, the last form of government.