Adam Smith, the father of modern economics, sought to demonstrate that markets (and economies) pre-existed the state, and hence should be free of government regulation. He argued (against conventional wisdom) that money was not the creation of governments. Markets emerged, in his view, out of the division of labour, by which individuals began to specialize in specific crafts and hence had to depend on others for subsistence goods. These goods were first exchanged by barter. Specialization depended on trade, but was hindered by the "double coincidence of wants" which barter requires, i.e., for the exchange to occur, each participant must want what the other has. To complete this hypothetical history, craftsmen would stockpile one particular good, be it salt or metal, that they thought no one would refuse. This is the origin of money according to Smith. Money, as a universally desired medium of exchange, allows each half of the transaction to be separated.
In a small economy where individuals specialize in trades, they may find the process of setting up a centralized currency and maintaining it an unnecessary burden in order to trade. One option may be to use a commodity to exchange value between parties that want to trade goods or services and this is why gold and silver have been useful forms of currency in many cultures and times. Another option may be to use a barter system to trade.