Revelation 12:3 - Matthew Poole's English Annotations on the Holy Bible

And there appeared another wonder in heaven; there appeared to John, being yet in his vision, another amazing sight, which was a sign or type of something differing from what it appeared like. And behold a great red dragon: see Revelation 12:7,9,17. Most judicious interpreters, by the great red dragon, understand the Roman emperors that first persecuted: the Christian church, of which Claudius was the first; yet some understand it of the devil, the old serpent; but the most and best interpreters understand it of the pagan emperors, by whom the devil did this work, called a great dragon, because of the vastness of that empire; a red dragon, for their cruelty against the Christians. Having seven heads; the Holy Ghost, Revelation 17:9, hath expounded these seven heads, by seven mountains. The ten horns are thought to signify the ten provinces belonging to that empire, the governors of which ruled like ten kings. It is expounded by ten kings, Revelation 17:12. Strabo tells us, that Augustus Caesar divided the whole empire into twenty provinces; ten of which, being more quiet, he gave to the people to govern, the other ten he reserved to his own government. The seven crowns are expounded by seven kings, Revelation 17:10, of which we shall speak more when we come so far.