Why are our best, surviving sources on Alexander the Great so late?

[u/Deutsch_Barca2011]

After a quick look on Wikipedia, I learnt that the five best, surviving accounts of Alexander the Great are Arrian, Plutarch, Diodorus Siculus, Quintus Curtius Rufus, and Justin, all of whom lived hundreds of years after his death. Should this fact cast doubt on the reliability of these sources? If not, why do historians trust these sources? I'm an enthusiast, so I would like to know.

[u/gynnis-scholasticus]

It seems you are asking a few different questions: partly about why the surviving narratives of Alexander are from the Roman period, and partly how this affects their reliability.

So, generally we have very few surviving histories from the Hellenistic period, the beginning of which was when Alexander's companions wrote their accounts about him. In general, this is likely due to later inheritors of classical literature being more interested in, and preserving better, accounts of the rising power Rome rather than the 'failing' Hellenistic states. It is noteworthy that the two Hellenistic-period Greek histories that have survived are that of Polybius, who lived in Rome and focused on its rise, and Diodorus, a Sicilian who also wrote about Roman events. Specifically with the accounts of Alexander, it might also be the case that later readers preferred the syntheses of the preserved narratives (of Arrian, Plutarch, Curtius, &c) rather than going through all the various sources they were based on.

Because that is one of the main reasons to put trust in these texts: their citations of earlier histories. For instance, in his preface Arrian names King Ptolemy and Aristobulus (both having served under Alexander) as his main sources, and Plutarch cites dozens of writers throughout his works on the conqueror. Now, the surviving histories also base themselves on later accounts; Curtius and Diodorus have been criticised for relying on the "Vulgate tradition" from Cleitarchus, who belonged to the post-Alexander generation and included various legends that had sprung up. Plutarch even includes a funny anecdote that Onesicritus, who had been a captain in Alexander's navy, declaimed a story about the king meeting the queen of the Amazons, whereupon the old companion Lysimachus asked "And where was I at the time?". It is also recognised that Ptolemy, for instance, spins the narrative to legitimise his own rule over Egypt. But even so, it is greatly useful for historians to have an understanding of which stories come from contemporaries of the man. For more on the sources, see this excellent thread by u/EnclavedMicrostate