The Works of Dionysius the Areopagite, tr. by John Parker, , at sacred-texts.com
Which is the first Order of the Heavenly Beings? which the middle? and which the last?
How many, and of what sort, are the Orders of the supercelestial Beings, and how the Hierarchies are classified amongst themselves, I affirm, the deifying Author of their consecration alone distinctly knows; and further, that they know their own proper powers and illuminations, and their sacred and supermundane regularity. For it is impossible that we should know the mysteries of the supercelestial Minds and their most holy perfections, except, some one might say, so far as the Godhead has revealed to us, through them, as knowing perfectly their own condition. We, then, will utter nothing as from ourselves, but whatever angelic visions have been gazed upon by the holy Prophets of God, we, as initiated in these, will set forth as best we can. The Word of God has designated the whole Heavenly Beings as nine, by appellations, which shew their functions. These our Divine Initiator divides into three threefold Orders. He also says that that which is always around God is first and is declared by tradition to be united closely and immediately, to Him, before all the rest. For he says that the teaching of the Holy Oracles declares, that the most Holy Thrones, and the many-eyed and many-winged hosts, named in the Hebrew tongue Cherubim and Seraphim, are established immediately p. 24 around God, with a nearness superior to all. This threefold order, then, our illustrious Guide spoke of as one, and of equal rank, and really first Hierarchy, than which there is not another more Godlike or immediately nearer to the earliest illuminations of the Godhead. But he says, that which is composed of the Authorities, and Lordships, and Powers is second; and, as respects the lowest of the Heavenly Hierarchies, the Order of the Angels and Archangels and Principalities is third.