In Code We Trust - NYTimes.com:
"When Caesar Augustus minted the denarius coin, around 15 A.D., he did so with a decree that it be made almost entirely of silver. But over the coming decades, as the financial health of the Roman Empire declined — largely because of its increasingly independent army, which demanded ever more money to subdue the rebellious provinces — the emperors began, slowly at first, mixing in copper to stretch the silver further. By 280 A.D., a denarius was 98 percent copper, with a thin silver wash on the surface. The implication was clear to every Roman: Here, in their hands, was a physical manifestation of the empire’s deepening desperation. Whatever proclamations the emperor might make, the coin told the truth."
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