According to medieval Christian theologians, the Angels are organized into several orders, or Angelic Choirs.

The most influential of these classifications was that put forward by Pseudo-Dionysius the Areopagite in the 4th or 5th century, in his book "The Celestial hierarchy". However, during the Middle Ages, many schemes were proposed, some drawing on and expanding on Pseudo-Dionysius, others suggesting completely different classifications (some authors limited the number of Choirs to seven). Several other hierarchies were proposed, some in nearly inverted order. Scholars of the Middle Ages believed that angels and archangels were lowest in the order because they were the most involved in the world of men and thus more susceptible to sin.

In The Celestial hierarchy and in the Summa Theologica the Catholic Church theologians drew on passages from the New Testament, specifically Ephesians 1:21 and Colossians 1:16 (considered by modern scholars to be very tentative and ambiguous sources in relation to the construction of such a schema), in an attempt to reveal a schema of three Hierarchies, Spheres or Triads of angels, with each hierarchy containing three Orders or Choirs.

From the comparative study of the Old Testament and New Testament passages, including their etymology and semantics, the above mentioned theological works (which contain variations), and esoteric Christian teachings, the descending order of rank can be inferred as following:
The Assumption of the Virgin by Francesco Botticini at the National Gallery London, shows three hierarchies and nine orders of angels, each with different characteristics:

• First Sphere (Old Testament sources)
o Seraphim
o Cherubim
o Ophanim (Thrones/Wheels)

• Second Sphere (New Testament sources)
o Thrones (Gr. thronos)
o Dominions (Gr. kuriotes)
o Powers (Gr. exousia)

• Third Sphere
o Principalities (Gr. arche)
o Archangels
o Angels

The Choirs in the second and third spheres, of the present hierarchical list, appear to be also united in pairs. The existence of these pairs of Orders is inferred through their etymological proximity and the apparent affinity in the description of their work-activity (cf. 1 Peter 3:22):

• Thrones and Dominions (Might, dunamis);
• Principalities and Powers (Powers, exousia; cf. Eph 6:12);
• Archangels and Angels (Angels, aggelos).

Note, however, that several variations of the hierarchical order may be found published through the last two millennia.

Hierarchies, Spheres or Triads of Choirs
First Sphere
Seraphim
The Seraphim (singular "Seraph"), mentioned in Isaiah 6:1—7 , serve as the caretakers of God's throne and continuously singing his praises: "Holy, holy, holy is the Lord of hosts. All the earth is filled with His Glory." It is said that they surround the throne of God, singing the "music of the spheres" and regulating the movement of the heavens as it emanates from God. It is also said that such a bright light emanates from them that nothing, not even other divine beings, can look upon them. It is said that there are four of them surrounding God's throne, where they burn eternally from love and zeal for God.
The Seraphim have six wings; two covering their face, two covering their feet, and two that they fly with.
Biblical references only refer to Lucifer as a cherub (never as a seraph). However some extra-bibilical sources provide fanciful notions of his being a seraph and unlike other seraphim who had six wings, Lucifer was featured to have had twelve wings, which supposedly further exemplified the regard to which God gave him above all the other angels prior to his fall.

Cherubim
The Cherubim (singular "Cherub") are beyond the throne of God; they are the guardians of light and of the stars. It is believed that, although they are removed from man's plane of reality, the divine light that they filter down from Heaven still touches the lives of living things.

They have four faces: one of a man, ox, lion, and eagle. The ox-face is considered the "true face", as later on in Ezekiel the ox's face is called a cherub's face (Chapter 10). They have eight conjoined wings covered with eyes, and they have ox's feet.

Cherubim are considered the elect beings for the purpose of protection. Cherubim guard Eden and the throne of God.

Their rank among angels is uncertain but they are always categorized in the First Sphere. Some believe them to be an order or class of angels; others hold them to be a class of heavenly beings higher than angels. Cherubim are said to have perfect knowledge of God, surpassed only by the love of the Seraphim.

The Cherubim are mentioned in Genesis 3:24; Ezekiel 10:17–20; and 1 Kings 6:23–28.

Ophanim
The Ophanim (Heb. owphan: Wheels, also known as Thrones, from the vision of Daniel 7:9) are unusual looking compared to the other celestial beings; They appear as a beryl-coloured wheel-within-a-wheel, their rims covered with hundreds of eyes.

They are closely connected with the Cherubim: "When they moved, the others moved; when they stopped, the others stopped; and when they rose from the earth, the wheels rose along with them; for the spirit of the living creatures [Cherubim] was in the wheels." (Ezekiel 10:17). In Esoteric Christianity they are called Lords of Flame.

De Coelesti Hierarchia refers the Thrones (from the Old Testament; Ezekiel and Daniel visions of the Thrones/Wheels) as the third Order of the first sphere, corresponding to the description of the Ophanim; the other two superior orders being the Cherubim and Seraphim. The Rosicrucian Cosmo-Conception refers that the "Lords of the Flame", the hierarchy of Elohim astrologically assigned to Leo, are the Thrones "because of the brilliant luminosity of their bodies and their great spiritual powers.", corresponding also to the description of the Ophanim; the other two superior hierarchies being also the Cherubim and Seraphim.

According to the mentioned esoteric Christian teachings, the three previous Hierarchies (Seraphim, Cherubim and Ophanim [Thrones/Wheels]) have already reached liberation, thus no longer active in the work of evolution.

Second Sphere
Angels of the Second Sphere work as heavenly governors.

Thrones
The Thrones (Gr. thronos) or Elders, also known as the Erelim, are a class of celestial beings mentioned by Paul of Tarsus in Colossians 1:16 (New Testament) and related to the throne of God the Father. They are living symbols of God's justice and authority. They come the closest of all Angels to spiritual perfection and emanate the light of God with mirror-like goodness. They, despite their greatness, are intensely humble, an attribute that allows them to dispense justice with perfect objectivity and without fear of pride or ambition. Because they are living symbols of God's justice and authority, they are called Thrones and have as one of their symbols the throne. These high celestial beings are mentioned again in Revelation 11:16.

The Thrones (Gr. thronos) may possibly be equated with the Lords of Wisdom, a hierarchy of Elohim astrologically associated to Virgo, presented in The Rosicrucian Cosmo-Conception. They inhabit, in Rosicrucian cosmology, the World of Divine Spirit, which is the home of The Father. According to this source, the Lords of Wisdom (here equated with the Thrones; thronos) and the higher Lords of the Flame (Thrones/Wheels: Ophanim) have worked together in a far past toward the development of mankind.

Virtues
The Virtues or Strongholds lie beyond the Ophanim (Thrones/Wheels). Their primary duty is to supervise the movements of the heavenly bodies in order to ensure that the cosmos remains in order.
The term appears to be linked to the attribute "Might", from the Greek root "dunamis" in Ephesians 1:21, which is also translated as "Virtue" (probably due to the powerful nature of these high celestial beings; see quotation below). They are presented as the celestial Choir "Virtues", in the Summa Theologica, and the theological conception of these highest beings appears to describe the same high Order, in touch with God the Father, called the Thrones (Gr. thronos).

From Dionysius the Areopagite:
"The name of the holy Virtues signifies a certain powerful and unshakable virility welling forth into all their Godlike energies; not being weak and feeble for any reception of the divine Illuminations granted to it; mounting upwards in fullness of power to an assimilation with God; never falling away from the Divine Life through its own weakness, but ascending unwaveringly to the superessential Virtue which is the Source of virtue: fashioning itself, as far as it may, in virtue; perfectly turned towards the Source of virtue, and flowing forth providentially to those below it, abundantly filling them with virtue."

Dominions
The Dominions (lat. dominatio, pl. dominationes), also known as the Hashmallim, hold the task of regulating the duties of lower angels. It is only with extreme rarity that the angelic lords make themselves physically known to mortals. Instead, they quietly concern themselves with the details of existence. They are also the angels who preside over nations.

The Dominions are believed to look like divinely beautiful humans with a pair of feathered wings, much like the common representation of Angels, but they are physically characterized from other groups as wielding orbs of light fastened to the heads of their sceptres or on the pommel of their swords.
The Dominions may possibly be equated with the Lords of Individuality, a hierarchy of Elohim astrologically associated to Libra, presented in The Rosicrucian Cosmo-Conception. They inhabit, in Rosicrucian cosmology, the World of Life Spirit, which is the home of Christ, The Son.
Leaders.

The Dominions are also translated from the Greek term "kuriotes" as Lordships, related to the Lord Christ-Jesus, and also Leaders. They are presented as the hierarchy of celestial beings Lordships in the De Coelesti Hierarchia.

Principalities
The Principalities (lat. principatus, pl. principatus) are shown wearing a crown and carrying a sceptre. Their duty also is said to be to carry out the orders given to them by the Dominions and bequeath blessings to the material world. Their task is to oversee groups of people. As beings related to the world of the germinal ideas, they are said to inspire living things to many things such as art or science.
The Principalities may possibly be equated with the Lords of Form, a hierarchy of Elohim astrologically associated to Scorpio, presented in The Rosicrucian Cosmo-Conception. They inhabit, in Rosicrucian cosmology, the World of Thought in the Region of Abstract Thought (higher region; the Christian Third Heaven), which is the home of Jehova, The Holy Spirit.

Rulers
The Principalities are also translated, from the Greek term "arche", as Princedoms and also Rulers (see Greek root in Eph 3:10).
These celestial beings appear to collaborate, in power and authority (as implied in their etymology source), with the Powers (Authorities). Rulers develop ideologies whereas Authorities write the documents and doctrines. Both Rulers (Principalities) and Authorities (Powers) are involved in formulating ideologies. However, Rulers are more focused on specific lines of thought whereas Authorities are all-encompassing.

Paul used the term rule and authority in Ephesians 1:21, and rulers and authorities in Ephesians 3:10. He may have been referring to the rulers and authorities of men or societies, instead of referring to angels.

Third Sphere
Angels who function as heavenly messengers and soldiers.

Powers
The Powers (lat. potestas (f), pl. potestates) are the bearers of conscience and the keepers of history. The angels of birth and death are Powers (?). They are academically driven and are concerned with ideology, philosophy, theology, religion, and documents pertaining to those studies. Powers are the brain trusts: a group of experts who serve as advisers and policy planners. They are also the warrior angels created to be completely loyal to God, thus the only order created after the fall. Some believe that no Powers have ever fallen from Grace but others say that not only have some of them Fallen, the Devil was believed to have been the Chief of the Powers before he Fell (see also Ephesians 6:12) Their duty is to oversee the distribution of power among mankind, hence their name.

The Powers may possibly be equated with the Lords of Mind, a hierarchy of Elohim astrologically associated to Sagittarius, presented in The Rosicrucian Cosmo-Conception. They inhabit, in Rosicrucian cosmology, the World of Thought in the Region of Concrete Thought (lower region; the Christian Second Heaven), which is the location of the human mind. This region is also described as the place where one of the three records of the Memory of Nature, covering the essence of a whole life or events, is kept-stored.

Paul used the term powers in Colossians 1:16 and Ephesians 1:21 but he may have used it to refer to the powers of nations, societies or individuals, instead of referring to angels.

Authorities
The Powers are also translated, from the Greek term "exousia", as Authorities (see Greek root in Eph 3:10).

These celestial beings appear to collaborate, in power and authority (as implied in their etymology source), with the Principalities (Rulers). Rulers develop ideologies whereas Authorities write the documents and doctrines. Both Authorities (Powers) and Rulers (Principalities) are involved in formulating ideologies. However, Authorities are all-encompassing whereas Rulers are more focused on specific lines of thought. Authorities specialize in putting those ideas into print and in producing actual documents.

Paul used the term rule and authority in Ephesians 1:21, and rulers and authorities in Ephesians 3:10. He may have been referring to the rulers and authorities of men or societies, instead of referring to angels.

Archangels
The word archangel comes from the Greek (archangelos), meaning chief angel. It derives from the Greek archo, meaning to be first in political rank or power; and aggelos which means messenger. This suggests that they are the highest ranking angels. The word is only used twice in the Bible: 1 Thessalonians 4:16 and Jude 1:9. Only Michael and Gabriel are mentioned by name in the Bible.
Michael is the only angel the Bible names expressly as an archangel. In Daniel he is referred to as "one of the chief princes". The word "prince" here is the ancient Hebrew word sar, which means: "a head person (of any rank or class), a chief, a general etc."

In most Christian traditions Gabriel is also considered an archangel, but there is no direct literal support for this assumption.

The name of the archangel Raphael appears only in the Deuterocanonical Book of Tobit (Tobias). Tobit is considered canonical by Catholics, Orthodox and some Protestants. Raphael said to Tobias that he was "one of the seven who stand before the Lord", and it is generally believed that Michael and Gabriel are two of the other seven. Another possible interpretation of the "seven" is that the seven are the seven spirits of God that stand before the throne.

They are said to be the guardian angels of nations and countries, and are concerned with the issues and events surrounding these, including politics, military matters, commerce and trade: e.g. Archangel Michael is traditionally seen as the protector of Israel and of the Ecclesia (Gr. root ekklesia from the New Testament passages), theologically equated as the Church, the forerunner of the spiritual New Israel.

Angels
The Angels, also known as the Malakhim (messengers or angels), are the lowest order of the angels, and the most familiar to men. They are the ones most concerned with the affairs of living things. Within the category of angels, there are many different kinds, with different functions. The angels are sent as messengers to men.

Choirs Scheme in the Medieval Theology
During the Middle Ages, many schemes were proposed, some drawing on and expanding on Pseudo-Dionysius, others suggesting completely different classifications (some authors limited the number of Choirs to seven). Several other hierarchies were proposed, some in nearly inverted order. Some of those schemes are here presented:
• Clement of Rome in Apostolic Constitutions (1st century):
o 1. Seraphim, 2. Cherumbim, 3. Aeons, 4. Hosts, 5. Powers, 6. Authorities, 7. Principalities, 8. Thrones, 9. Archangels, 10. Angels, 11. Dominions.

• St. Ambrose in Apologia Prophet David, 5 (4th century):
o 1. Seraphim, 2. Cherumbim, 3. Dominations, 4. Thrones, 5. Principalities, 6. Potentates (or Powers), 7. Virtues, 8. Angels, 9. Archangels.

• St. Jerome (4th century):
o 1. Seraphim, 2. Cherubim, 3. Powers, 4. Dominions (Dominations), 5. Thrones, 6. Archangels, 7. Angels.

• Pseudo-Dionysius the Areopagite in De Coelesti Hierarchia (ca. 5th century):
o First sphere: 1. Seraphim, 2. Cherumbim, 3. Thrones;
o Second sphere: 4. Authorities, 5. Lordships, 6. Powers;
o Third sphere: 7. Principalities, 8. Archangels, 9. Angels.

• St. Gregory the Great in Homilia (6th century)
o 1. Seraphim, 2. Cherubim, 3. Thrones, 4. Dominations, 5. Principalities, 6. Powers, 7. Virtues, 8. Archangels, 9. Angels.

• St. Isidore of Seville in Etymologiae (7th century):
o 1. Seraphim, 2. Cherubim, 3. Powers, 4. Principalities, 5. Virtues, 6. Dominations, 7. Thrones, 8. Archangels, 9. Angels.

• John of Damascus in De Fide Orthodoxa (8th century):
o 1. Seraphim, 2. Cherubim, 3. Thrones, 4. Dominions, 5. Powers, 6. Authorities (Virtues), 7. Rulers (Principalities), 8. Archangels, 9. Angels.

• St. Thomas Aquinas in Summa Theologica (1225-1274):
o 1. Seraphim, Cherubim, and Thrones;
o 2. Dominations, Virtues, and Powers;
o 3. Principalities, Archangels, and Angels.

• Dante Alighieri in The Divine Comedy (1308-1321)
o 1. Seraphim, 2. Cherubim, 3. Thrones, 4. Dominations, 5. Virtues, 6. Powers, 7. Archangels, 8. Principalities, 9. Angels.

Jewish Angelic hierarchy
Maimonides, in his Yad ha-Chazakah: Yesodei ha-Torah, counts ten ranks of angels in the Jewish angelic hierarchy, beginning from the highest:
Rank Angel Notes
1 Chayot Ha Kadesh
2 Ophanim
3 Erelim See Isaiah 33:7
4 Hashmallim See Ezekiel 1:4
5 Seraphim
6 Malakhim Messengers, angels
7 Elohim "Godly beings"
8 Bene Elohim "Sons of Godly beings"
9 Cherubim See Talmud Hagigah 13b
10 Ishim "manlike beings", see Daniel 10:5)

Alternative hierarchy Structures found in certain Manuscripts

Angel Appearences

The following are descriptions of how these orders are commonly portrayed in religious art:

Seraphim - a child's head and wings depicted, usually in red, and may have a candle; or in human form with three pairs of wings.
Cherubim - a child's head and several pairs of wings, usually blue or gold, with a book.

The following are usually of human shape, dressed in flowing white and gold garments from which large gold wings protrude, either outstretched or folded, and they are commonly barefooted:

Thrones - may hold a throne.
Dominions - may be crowned and hold an orb and scepter.
Virtues - hold a rose or a lily.
Powers - may be in armor.
Principalities, Archangels, and Angels - unless named, have a youthful, feminine appearance.

Reference:

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