 Iamblichus’ On the Pythagorean Life is largely a compilation of earlier sources but, unlike Porphyry, he does not usually identify them. Rohde (1871–1872) argued influentially that  On the Pythagorean Life was largely a compilation from two sources: Nicomachus’ Life of Pythagoras and a life of Pythagoras by Apollonius of Tyana. O’Meara argues that this underestimates both the extent to which Iamblichus reworked his sources for his own philosophical purposes and the variety of sources that he used (O’Meara 2014, 412–415). A particularly clear example of Iamblichus’ distintive development of ideas found in earlier sources can be seen in his treatment of the doctrine of the harmony of the spheres (O’Meara 2007). It is also true that the remaining books of On Pythgoreanism use a variety of sources. Book Two, Protreptic to Philosophy, is an exhortation to philosophy in general and to Pythagorean philosophy in particular and relies heavily on Aristotle’s lost Protrepticus. Book Three, On General Mathematical Science, deals with the general value of mathematics in aiding our comprehension of the intelligible realm and is followed by a series of books on the specific sciences. The treatment of arithmetic in Book IV takes the form of a commentary on Nicomachus’ Introduction to Arithmetic. Books V-VII then dealt with arithmetic in physics, ethics and theology respectively and were followed by treatments of the other three sciences in the quadrivium: On Pythagorean Geometry, On Pythagorean Music and On Pythagorean Astronomy. Iamblichus was particularly interested in Pythagorean numerology and his section on arithmetic in theology is probably reflected in the anonymous treatise which has survived under the title Theologoumena Arithmeticae and which has sometimes been ascribed to Iamblichus himself. It appears that here again Iamblichus relied heavily on Nicomachus, this time on his Theology of Arithmetic.