Other
University of Exeter: Comparative Chronology of Money: Ancient Times/present Day
A timeline of coinage history in Ancient Rome and how debasement helped lead to the downfall of the Roman Empire.
Other
Chicago Coin Club: Eight Hundred Years of Roman Coinage
Nearly halfway through this page under the subtitle, "Disintegration of the Monetary System" is a discussion of the monetary collapse and the efforts of subsequent emperors to restore the coinage.