A fascinating short excerpt from a new study that estimates war and population change in Ancient Rome from finds of stashed coins.
It turns out that the coin hoards are a surprisingly good guide to human behaviour:
The reasons for this correlation are not hard to fathom. People tend to hide their valuables in times of violence and danger. Emergency hoards would later be recovered by the owners unless they had been killed or driven away. As a result, the greater the intensity of warfare, the more hoards are left in the ground to be discovered by archaeologists. For this reason, the time-specific deposition rate of hoards serves as an index of internal instability caused by violent conflict and dislocation.
Coins are useful because, of course, they’re dated. So in other words, finding lots of unrecovered coin stashes from a particular time period suggests there was a lot of war.
The researchers used this measure of war intensity in Ancient Rome to estimate population changes. Neat.
Link to full text of study.
Mind Hacks 
As David Graeber argues in Debt: The First 5,000 Years, cash economies and coinage are originated by the need to pay soldiers (or trading in slaves.) I would add that this coinage is usually quickly deflated. This might hugely affect the studies conclusions.
Wartsan-all”coinage is usually quickly deflated”
What? old coins usually had gold or silver in them so they can’t BE deflated.
My comment…
The rate of inflation has made the value of a copper coin too expensive to produce in relation to its value so countries have stopped producing the penny.
The final Canadian penny was minted on May 4, 2012
http://en.wikipedia.org/wiki/Penny_debate_in_the_United_States
When will this happen to the 5 cent piece, ten cent piece and the rest of metal currency?
Deflated through debasing. The intrinsic value of Roman coins changed as they were diluted or “debased” over time. Therefore, it is important to consider the effect of debasing the silver content of Roman coins from 100% in 68 AD to less than 10% by 268 AD, relative to market values.
http://www.virginia.edu/artmuseum/VirtualExhibitions/Coins/hoard_analysis.html
http://articles.businessinsider.com/2011-05-20/wall_street/30064643_1_currency-decline-and-fall-love