Antigonus II, a student of Zeno of Citium, spent most of his rule defending Macedon against Epirus and cementing Macedonian power in Greece, first against the Athenians in the Chremonidean War, and then against the Achaean League of Aratus of Sicyon. Under the Antigonids, Macedonia was often short on funds, the Pangaeum mines were no longer as productive as under Philip II, the wealth from Alexander's campaigns had been used up and the countryside pillaged by the Gallic invasion. A large number of the Macedonian population had also been resettled abroad by Alexander or had chosen to emigrate to the new eastern Greek cities. Up to two-thirds of the population emigrated, and the Macedonian army could only count on a levy of 25,000 men, a significantly smaller force than under Philip II.