In the late Middle Ages peasants disrupted the power structure of fiefdoms by using locally minted currencies tied to grain in lieu of bartering. Farmers received receipts in the form of foil with a perforation for each unit of grain they brought to a grain store. Pieces of that receipt could be torn off and used as currency to purchase goods, with the understanding that the grain receipt could be redeemed for a unit of grain from the grain store. This enabled local trade to flourish and decreased the dependency most people had on the vertical power structure controlled by a ruling class.
The value of grain quickly decreases because it is easily and quickly destroyed. The value of a grain receipt decreased as its corresponding amount of grain was lost. A currency whose value quickly decreases is only good for the "flow" of marketplace transactions, not storage. This made it difficult for the rich to remain rich. Many people who acquired wealth invested it in a more durable asset, such as a cathedral, whose value would last longer than grain and would potentially yield a return on investment for many years. This helps explain why so many cathedrals were created in the era prior to the Renaissance (the "Age of Cathedrals").
In order to retain control over society, members of the ruling class put a stop to this grain-backed currency, and replaced it with one that would be most beneficial to themselves, not the general population. Wealth is easier to store if the currency is backed by inorganic material, such as gold and silver, because it does not decay and rats will not eat it, etc. In other words, they implemented a currency designed for storage and accumulation, not as an expedient for the flow of goods between hands in the marketplace.
Fast forward a few centuries to the present. In response to the failures of the Euro, such as in many Greek villages, and the ubiquitous presence of the Web, new forms of virtual currency are being used. These currencies take many forms, such as earning redeemable points by rendering services for people in the community. What they have in common is that they are designed for flow, not storage. The Web has enabled the common man to once again have a currency designed for his own benefit, not one designed to assist a ruling class to remain in power by virtue of their existing wealth.