History can offer us some valuable lessons about what we can expect in the future when it comes to how we pay for goods and services, that is, money. Since 1450, we have seen six reserve currencies: the Portuguese real (1450-1530), the Spanish real (1530-1640), the Dutch guilder (1640-1720), the French franc (1720-1815), the pound sterling (1815-1920) and finally the US dollar from 1921 to the present.