One cannot take these graphs at face value, for example, the long $ decline from 1933 to the present has also been the Pax Americana where the US has dominated geopolitics. Also, the Roman denarius was a commodity based currency, while the US$ is a fiat currency backed by US government taxing power over US assets.
But the larger issue of the costs of empire over time are instructive. One should dig deeper in analysis, but not be too complacent. Especially in light of the currency manipulations of the current age.