After these kingdoms, in ancient Rome, after its first kings and consuls, under Caesar Augustus the Roman Empire became universal. It was sustained by its impious kings until Constantine the Great.
The seven kings must be understood in the same way. The difference in gender among the words heads, mountains, and kings should not hinder their common interpretation.
For in Holy Scripture names are often used quite indifferently, masculine for feminine and the reverse. For example, "Ephraim is a heifer taught to love threshing," and elsewhere, "Ephraim is a dove without heart" (Hos 10:11; 7:11).
And according to the Apostle the Theologian: "There are three that bear witness on earth, the spirit, the water, and the blood, and these three are one" (1 Jn 5:8). And according to Solomon: "a goat, a rooster, and a king speaking before the people" (Prov 30:31-32).
Thus the seven heads signify cities. The seven mountains signify seven conditions in which, at different times, they surpassed other places of the earth not in population but in glory.
The kings likewise signify either places made illustrious as the dwelling places of a king, or the first kings in each of the places mentioned. Their kingdoms are also called by their names.
Thus the Assyrian kingdom is named from Ninus, the Median from Arbaces, the Babylonian from Nebuchadnezzar, the Macedonian from Alexander, ancient Rome from Romulus, and new Rome from Constantine.