Coinage
These factors led to the metal itself being the store of value: first silver, then both silver and gold, and at one point also bronze. Now we have copper coins and other non-precious metals as coins. Metals were mined, weighed, and stamped into coins. This was to assure the individual taking the coin that he was getting a certain known weight of precious metal. Coins could be counterfeited, but they 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 metal, and thus the value of a coin could be determined, even if it had been shaved, debased or otherwise tampered with.
Most major economies using coinage had three tiers of coins: copper, silver and gold. Gold coins were used for large purchases, payment of the military and backing of state activities. Silver coins were used for midsized transactions, and as a unit of account for taxes, dues, contracts and fealty, while copper coins were used for everyday transactions. This system had been used in ancient India since the time of the Mahajanapadas. In Europe, this system worked through the medieval period because there was virtually no new gold, silver or copper introduced through mining or conquest. Thus the overall ratios of the three coinages remained roughly equivalent.