“WE KNOW on the authority of Scripture that there are nine orders of angels, viz., Angels, Archangels, Virtues, Powers, Principalities, Dominations, Throne, Cherubim and Seraphim. That there are Angels and Archangels nearly every page of the Bible tell us, and the books of the Prophets talk of Cherubim and Seraphim. St. Paul, too, writing to the Ephesians enumerates four orders when he says: 'above all Principality, and Power, and Virtue, and Domination'; and again, writing to the Colossians he says: 'whether Thrones, or Dominations, or Principalities, or Powers'. If we now join these two lists together we have five Orders, and adding Angels and Archangels, Cherubim and Seraphim, we find nine Orders of Angels.”
~Pope St. Gregory I ("the Great"): Homilies, 34.