Porphyry also wrote widely on astrology, religion, philosophy, and musical theory. He produced a "History of Philosophy" ("Philosophos historia") with "vitae" of philosophers that included a life of his teacher, Plotinus. His life of Plato from book iv exists only in quotes by Cyril of Alexandria. His book "Vita Pythagorae" on the life of Pythagoras is not to be confused with the book of the same name by Iamblichus. His commentary on Ptolemy's "Harmonics" ("Eis ta Harmonika Ptolemaiou hypomnēma") is an important source for the history of ancient harmonic theory.