While a few fragments exist, there is no surviving historical work which dates to the hundred years following Alexander's death. The works of the major Hellenistic historians Hieronymus of Cardia (who worked under Alexander, Antigonus I and other successors), Duris of Samos and Phylarchus which were used by surviving sources are all lost. The earliest and most credible surviving source for the Hellenistic period is Polybius of Megalopolis (c. 200-118), a statesman of the Achaean League until 168 BCE when he was forced to go to Rome as a hostage. His Histories eventually grew to a length of forty books, covering the years 220 to 167 BCE.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): Where was Polybius from?
Megalopolis