Roman coinage is another rich source of finds. Roman coinage is a text-book example of how to mis-manage a currency; the coins that were used were all intrinsic-value coins, so the silver denarius you had in your pocket was valuable because it was silver, not really because the Government said it was. However, progressive emperors had a recurring habit of gathering as much coinage of the previous emperor as they could find, melting it down and debasing it, then re-issuing their own coins which were supposedly as good as the previous ones, but were not actually as good. People even went to the extremes of acid-etching coins to make them look more silvery and better than they actually were.

This meant that over time, old Roman coins stayed in circulation because they were more valuable than the later ones, and hoarding of coin was commonplace. At one point the Emperor Nero even tried to legally prop up the debased value of his coinage, but got forced to back down on this foolery.

An interesting contrast to this rampant stupidity is the behaviour of the early English kings, who had a longstanding policy of maintaining silver content of their coins and who also tended to call in old coinage to melt it down, but always made the re-issued coins a shade heavier than the old ones. This strongly discouraged hoarding, since a new silver penny was actually more valuable than an old one, hence hoards lost value over time.

Finally, the last great source of metal detector finds is rubbish. People have always been messy, and rubbish is everywhere; a pest to some, a valuable archaeological resource to others, and if you happen on a good early Victorian bottle dump you can actually make quite nice money for good unbroken early examples.