I once believed that Diodorus switched sources at his book boundaries, but now I know that is not in general true. It is in fact very likely, though not certain, that the switch beween Cleitarchus and Hieronymus is signalled by the geographical digression in Diodorus 18.5. The arguments for this are many and varied, but, in particular, I find it striking that some of the stipulations of the Last Plans in Diodorus 18.4 are also in Curtius 10.1.17-19 (e.g. the campaign against the Carthaginians), where he is clearly following Cleitarchus. Jane Hornblower also reached this same conclusion in her magisterial and unrivalled study of Hieronymus of Cardia pp. 80-97, although for different reasons than me. Therefore the use of pyra by Diodorus is in all probability from Cleitarchus. It is true that this way of using pyra is rather Homeric in its inspiration, but that is not surprising in Cleitarchus, who is very strong on the parallel between Alexander and Achilles.agesilaos wrote:Without re-hashing the whole pyre thread, it must be bourne in mind that the two mentions of the 'Pyra' occur in two separate books, XVII based on Kleitarchos, possibly directly, in which case as a non eye-witness he possibly took his description from Ephippos' pamphlet and Book XVIII which is probably based on Hieronymos of Kardia (possibly via an intermediate source), the fantasist clearly describes a pyre for burning and the tradition based upon his works continued to as evidenced by Polyainos; the probable eye-witness of events in Babylon says it was not built and the structure described by Diodoros would have required the hand of God to both build and then erase completely from the archaeological record.
To answer amyntoros's question about how we know sources are following Cleitarchus: this comes from the einquellenprinzip, the idea that Diodorus uses one source at a time for his Library of History. He therefore preserves a series of earlier historical works in epitome. The Germans who very efficiently and methodically founded quellenforschung (source research in historiography) then asked themselves who Diodorus was epitomising in Book 17. They had assiduously collected named fragments of the works of most of the earlier historians that he might have been epitomising, so they just counted the proportion of those fragments for each earlier author that have a direct parallel in Diodorus 17. Cleitarchus wins easily. That statistical argument, despite being challenged frequently for more than a century, still stands more or less unscathed today and much else has been added to support it. The next step was to note that there is an extreme amount of commonality between Diodorus and Curtius: it is deeply obvious that they had a common source, but Curtius cannot be following Diodorus, because he is both later and more detailed. Similar source studies show unequivocally that the Metz Epitome is virtually pure Cleitarchus (in severe epitome) and that Justin/Trogus is a slightly less direct derivative of Cleitarchus. Plutarch used Cleitarchus, but he mixed in a lot of material from many other sources too.
Best wishes,
Andrew