PAPER MONEY.
As wealth increases, owning a large number of gold and silver coins becomes a security problem. As coins are portable, they are also easy to steal. The next step in the development of money was for people to leave their surplus gold and silver coins with a goldsmith who had a reputation for honesty and who operated premises which were secure. The goldsmith would give a receipt, which would entitle the owner to withdraw their coins when they needed them. This was the beginning of paper money.