When Alexander set out to conquer the Persian Empire, he borrowed much of the money with which to pay and provision his troops, and he minted his first coins, used to pay his creditors and continue to support the money, by melting down gold and silver plundered after his initial victories. However, an expeditionary force needed to be paid, and paid well: Alexander’s army, which numbered some 120,000 men, required half a ton of silver a day just for wages. For this reason, conquest meant that the existing Persian system of mines and mints had to be reorganized around providing for the invading army; and ancient mines, of course, were worked by slaves. In turn, most slaves in mines were war captives. Presumably most of the unfortunate survivors of the siege of Tyre ended up working in such mines. One can see how this process might feed upon itself.

-- Debt: The First 5,000 Years