being "issued", what we mean is that wealth, in the form of precious metal, was turned into coins with the sole purpose of being spent -on the army, new palaces, bribes and scribes, etc. Thus the expansion of new territories meant more captured silver and gold which could finance the building of new temples to the glory of Rome, and fortuitously a shot in the arm for the economy of the Empire. This happy state of affairs lasted lasted in the Roman Empire until around the end of the second century A.D.
However, the Empire could not expand forever and nor could the supply of precious metal. The conquered peoples sought to get their territory back; 'barbarians' started to move in. The emperors needed money to fight them and there was only so much that could be extorted from tax-payers. The Roman silver denarius was based on a weight of 1/96th of a Roman Pound. To make each Pound of silver go further the silver was diluted with a base metal, such as copper, a process known as 'de-basement'. Thus they could get more denarii from the same amount of silver. The problem was that an old denarius then had a higher intrinsic value than a new denarius, even though they both had the same face value. This period of de-basement caused it's own problems and affected the pattern of hoarding.
Gold coins in the Roman period were never, or rarely ever, de-based but their size and hence their weight were changed. This was partly to retain a fixed relationship between gold and silver, but this was hardly ever achieved for long as the bullion values of the two metals would eventually diverge, and gold coins remained effectively bullion.
The act of hoarding in ancient times is popularly thought to be the hiding away of particularly valuable items, and especially older gold and silver coins that may have increased in value due to the de-basement of newer coins. However, a little thought should cause us to modify that theory. Firstly, from Republican times to the end of of the second century, the weight and fineness of the denarius was fairly constant. Newly minted coins were 'charged'; that is to say, if a Roman Pound of silver was hypothetically sold to the mint, the mint would manufacture 96 denarii but pay the seller, say, 90 denarii. This created a profit for the mint but also prevented denarii in circulation being melted down for profit. Clearly, then, there was no particular incentive to melt down or hoard old or new coins as a means of making a profit. It also follows that old denarii would have been just as acceptable as new ones for circulation. As we shall see below, denarii from a wide range of dates were hoarded and must therefore have also been circulating. Some issues may have been officially de-monetised, but records of official recalls have not survived the passing of time, although it is known that Republican denarii were officially de-monetised during the reign of Trajan. However, de-monetisation of coins is not a hundred percent achievable when the coins are worth their own weight in silver, unless they can be brought to a mint, which Britain did not have, and clearly some survived.
From the end of the second century, de-basement set it, so clearly hoards after that date could have been used to keep back better silver, but even here mixtures of old and new coins are still found together together. Even when the coinage was de-based to virtually zero intrinsic value, coins were still being hoarded.
The obvious conclusion from the above is that coin hoards should be be considered as the equivalent of today's bank accounts, with an outflow of coins as well as an inflow. Although banks, of sorts, did exist in Roman towns, outside of them people had to carry their money around with them or hide it somewhere safe, such as a locked, immobile chest. The other place to hide money was in the ground, perhaps in a purse or other container. These are, of course, the hoards that are found today.
People were, perhaps unconsciously, selective about what they hoarded. That is to say, when they paid for something they tended to use the smallest,