This is wrong. You Need to read Graebers History of Money
Maybe you need to read von Mises "the theory of money and credit" ?
In modern times gold was reserve money and mainly used for international trade but inside the nation, money was largely credit money. Credit money and metal money have always coexisted. Gold itself wasn't the money it's the coins with stamp of the king on it. In essence money has always been a creature of law whenever there is a state
Do you know where "dollar" comes from ? It's a mass unit of gold.
Edit: I'm wrong, it was an amount of silver: 24 grams.