The capture of the Achaemenid treasuries in 331–330 BCE by Alexander the Great in Persepolis and Susa marked the demise of the 300-year-old Persian Empire and the advent of Hellenistic kingdoms. Alexander seized the equivalent of about 5000 tons of silver, which represented the accumulated tributes paid by subjugated people from the Aegean Sea to the Indus to their Achaemenid rulers. Die studies show that this gigantic amount of silver, the so-called Persian mix, had been used to produce most of the coinage of Alexander the Great himself and to an even greater extent those of the Diadochi, his successors. What remains to be understood is the origin of the silver of this immense treasure. Lead isotope abundances determined on both Persian sigloi and alexanders struck from Achaemenid silver trace the bullion source to the southern Aegean, Macedonia, and Thrace. Lead in pseudo-coinage from early Indian kingdoms is isotopically different from the rest, which attests to a limited Indian contribution to the Achaemenid treasuries. Studies of Iron Age hoards from the Levant leave open the possibility that the making of the Persian mix may have predated the Achaemenid expansion of the seventh century BCE. We speculate on the motivations of such massive hoarding by the Persian kings and on its economic implications.