On the Heavenly Hierarchy

Saint Dionysius the Areopagite lived in the 1st century AD in Athens. He was elected a member of the Areopagus and became a companion of the Apostle Paul, who appointed him Bishop of Athens. He witnessed a solar eclipse at the moment of the crucifixion of the Lord Jesus Christ and was present at the burial of the Most Holy Mother of God.

The book "On the Heavenly Hierarchy" contains an angelic classification through triads based on their closeness to God. Seraphim, Cherubim, and Thrones belong to the highest hierarchy; Dominions, Virtues, and Powers belong to the middle; and Principalities, Archangels, and Angels belong to the lowest. This division did not correspond to the understanding of the world of angels in the Old Testament but was adopted by some subsequent theologians, including Thomas Aquinas, Gregory Palamas, and others.