In fact, Roman gold currency was invented primarily to pay the troops. As a result gold as a currency only circulated around regions where the military was figh

In fact, Roman gold currency was invented primarily to pay the troops. As a result gold as a currency only circulated around regions where the military was fighting, and in peaceful areas far from warfare the usual methods of debts and IOUs were used to pay for things. If you’re still curious, read Graeber’s “Debt: The First 5000 years” which delves into the Roman monetary system in detail.