Proclus headed the Platonic Academy at Athens in the fifth century, in the closing period when a pagan philosophical school was operating inside a Christian empire, and his instinct was to codify everything before it was lost.
The Elements of Theology is the extreme case: two hundred and eleven propositions, each demonstrated from those before it, laying out the procession of all things from the One and their return to it in the form of a geometry. Between the One and the intelligible world he inserted the henads, unities that are the gods of traditional cult given a metaphysical office, a move that let him keep the entire pagan pantheon inside a rigorous monistic system rather than choosing between them.
Two consequences reach the later tradition. The first is structural: his ranked orders of gods, angels, daemons and heroes are the model for the elaborate hierarchies of medieval angelology and of Renaissance and modern occult cosmology. The second is a transmission accident of the first importance. The Christian writer known as Dionysius the Areopagite adapted Proclus's scheme into a Christian celestial hierarchy of nine angelic orders, and because he was believed until the Renaissance to be the Athenian converted by Paul, that hierarchy carried apostolic authority through the whole Middle Ages. A great deal of Christian angelology is Proclus, unattributed.