Hierarchy of Angels

The most influential Catholic angelic hierarchy was that put forward by Pseudo-Dionysius the Areopagite in the 5th or 6th century in his book De Coelesti Hierarchia (On the Celestial Hierarchy). Dionysius described nine levels of spiritual beings which he grouped into three orders:[1][2][3]

• Highest ordersSeraphimCherubimThrones
• Middle ordersDominionsVirtuesPowers
• Lowest ordersPrincipalitiesArchangelsAngels

During the Middle Ages, various schemes were proposed, some drawing on and expanding on Pseudo-Dionysius, others suggesting completely different classifications.

Pseudo-Dionysius (On the Celestial Hierarchy) and Thomas Aquinas (Summa Theologiae) drew on passages from the New Testament, specifically Ephesians 1:21 and Colossians 1:16, to develop a schema of three Hierarchies, Spheres or Triads of angels, with each Hierarchy containing three Orders or Choirs.

(Wikipedia)