Currency
Coinage

The prevalence of metal coins possibly led to the metal itself being the store of value: first copper, then both silver and gold, and at one point also bronze. Today other non-precious metals are used for coins. Metals were mined, weighed, and stamped into coins. This was to assure the individual accepting the coin that he was getting a certain known weight of precious metal. Coins could be counterfeited, but the existence of standard coins also created a new unit of account, which helped lead to banking. Archimedes' principle provided the next link: coins could now be easily tested for their fine weight of the metal, and thus the value of a coin could be determined, even if it had been shaved, debased or otherwise tampered with (see Numismatics).

Most major economies using coinage had several tiers of coins of different values, made of copper, silver, and gold. Gold coins were the most valuable and were used for large purchases, payment of the military, and backing of state activities. Units of account were often defined as the value of a particular type of gold coin. Silver coins were used for midsized transactions, and sometimes also defined a unit of account, while coins of copper or silver, or some mixture of them (see debasement), might be used for everyday transactions. This system had been used in ancient India since the time of the Mahajanapadas. The exact ratios between the values of the three metals varied greatly between different eras and places; for example, the opening of silver mines in the Harz mountains of central Europe made silver relatively less valuable, as did the flood of New World silver after the Spanish conquests. However, the rarity of gold consistently made it more valuable than silver, and likewise silver was consistently worth more than copper.
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