Explanation: The top photo is of a coin of the Principate era, the Roman Empire as we think of it. The bottom photo is of a coin in the Byzantine Empire. Artistic standards... dropped a bit.
In addition, while we think of money as very normal and natural, the fact is that a monetized economy is a very fragile thing - over the course of the collapse of the Roman Empire, the demonetization of the economy was near-total, resulting in a return to barter and, especially, clientistic economic relations rather than free exchange.