I suspect the first three horns were:
Constantine the Great, 306-337
Theodoric the Great, 488-526
Justinian the Great, 527-565
These three gave their authority and power to the little horn who grew up among them, the office of the papacy. It is from the reign of Pope Gregory I, or Gregory the Great (590-604), that the little horn deposed the three horns who came before him, and established (his own) ecclesiastical authority as superior to their civil authority.
Charles the Great (“Charlemagne,” reigned as King of the Franks 768-814, as Emperor of the Romans 800-814), his father, Pepin the Short, may in fact be one of the horns: he was crowned Patrician of the Romans by Pope Stephen II in Paris, in 754, and this was the first time in recorded history that a civil ruler was crowned by the pope. King Pepin then attacked the Lombards, a German tribe who had overrun northern Italy and was seizing church lands. He defeated him, returned the lands to the church, and gave the pope more provinces besides, known in history as the Donation of Pepin. This gift marks the establishment of the Papal States and the pope as a civil ruler in his own right. Pepin furthermore consolidated the territories held by modern France, more or less, under his sole rule. The reason I am not sure if he was one of the ten horns, is that he did not rule an empire outside of his natural dominions, as we have seen that the other horns have done.
His son, Charlemagne, however, did increase his holdings so greatly (map), that France, Germany, Italy, and all the states formerly belonging to the Holy Roman Empire, list him in their king lists as Charles I. He continued his father’s policy of war with the Lombards on behalf of the pope, war with the Saracens (Mohammedans who had conquered Spain), and war with the remaining pagan German tribes who surrounded his dominions, forcibly converting them to the Roman church upon their conquest.
In 795 a new pope was elected, Leo III. After only a few years, he was accused of adultery and perjury, and a mob tried to gouge out his eyes and tear out his tongue. He was rescued by the knights of Rome, deposed, and sent to a monastery. Leo escaped and made his way to Charlemagne to plead his case. Charlemagne believed it was his duty to uphold the church, and the pope’s duty, in turn, to pray for the king and for victories for his army. Charlemagne called the parties in the dispute to present their case, but could not render a decision as there was no proof. He had Leo escorted back to Rome, and in 800, went there himself to finalize the matter.
Upon Leo’s sworn oath of his innocence, he was reinstated. Two days later was Dec 25, the date of the traditional Roman festival honoring the nativity of the sun god, but which the office of the papacy had changed to the nativity of the Son of God. Pope Leo III crowned Charlemagne with the imperial crown of the old Roman emperors, and declared him the sixty- eighth Emperor of Rome (the sixty- seventh being the emperor who was killed by the German king Odoacer when he brought about the fall of Rome in 476 ad). Interestingly enough, almost all of the old Roman emperors believed that they were the sun god incarnate, which is why sacrifices were made to Caesar.
I don’t know that either Leo or Charlemagne had all this symbolism figured out in advance, with the dates, and acted on it. I do believe the scarlet dragon, however, whose power and authority both Leo and Charlemagne wielded, did. With Charlemagne’s coronation as Imperator Augustus Romanorum (Emperor Augustus of the Romans) the Holy Roman Empire, which covered most of Europe, as these were the lands conquered and ruled by Charlemagne, was formed.
The French and German monarchies descending from the empire ruled by Charlemagne as Holy Roman Emperor cover most of Europe. In his acceptance speech of the Charlemagne Prize Pope John Paul II referred to him as the Pater Europae (“father of Europe”): his empire united most of Western Europe for the first time since the Romans, and the Carolingian renaissance encouraged the formation of a common European identity. — Charlemagne, Wikipedia
The Byzantine empire, the old Eastern Roman empire, objected to this act, as they considered themselves the emperors of the West as well as the East, but they did not have the power to do anything about it, so it stood. The beast from the land (the papacy) created an image (Holy Roman Empire) of the beast from the sea (Roman empire), healing its mortal wound and bringing it back from the dead.
Christine’s book The Revelation of Jesus Christ Revealed, based on these studies but greatly expanded, is now available at Revelation Revealed Online. You may also be interested in reading the Book Extras and joining in on the Discussion.