Dionysius can be considered the founder of Christian mysticism. Indeed, the term "mysticism" itself in its present usage derives from him.

His "De Celestia Hierarchia" translated the Neoplatonic hierarchy of intermediate beings between man and the Godhead into the Christian paradigm and established the idea of Angelic hierarchies in Medieval and Renaissance Europe.

His treatise "On the Divine Names", which was just as important (or sometimes even more important) in the history of religious thought than the "De Celestia Hierarchia".  It was fundamental in the current of "apophantic" theology, that is, the doctrine that we can say more about what God is NOT than about what He is.

In the early 20th century Dionysius's angelogy was revived and given new interpretations by the esoteric philosopher and occultist, Rudolph Steiner.

- Dionysius the Areopagite -  Dionysius the Areopagite, Saint - very short but still useful entry - mirror - mirror - mirror Platonic Elements in Pseudo-Dionysius Anti-Manichaean Ontology - Professor Constantine Scouteris - University of Athens Dept. of Theology - on-line essay - rather difficult going but contains a lot of useful information Pseudo-Dionysius home page - not much here last time I checked The Angelic Hierarchy - based on the nine choirs of angels as described in "De Celestia Hierarchia", but employs other material as well

Esoteric