score:4
The correct term for this is Debas*m*nt of the currency. The Wikipedia article on Roman Currency has details.
To summarise, the basic coin was the denarius, introduced in 211BC. Its size and the amount of silver in it gradually shrank over time; debas*m*nt of the coins was a fairly continuous process. The exact reasons for it aren't clear, but shortages of precious metals, and inadequate state finances probably had a lot to do with it. Debas*m*nt usually increased when the empire was weak.
Upvote:3
I wanted to expand on my comment; the traditional formulation of the economic principle is "Inflation is a tax for which nobody has to vote." In an autocracy like the Roman Empire, the maxim would be slightly adjusted, "Debas*m*nt is a way of funding the government without generating opposition from strong stakeholders."
Debas*m*nt reduces the buying power of the individual and shifts that buying power to the state - it reduces the wealth of everyone who stores wealth in coin. Like most "flat" taxes, it is regressive and has a greater impact on the poor. Like most flat taxes, it is also easier for the wealthy and powerful to minimize the impact of the tax. (when debas*m*nt is imminent, shift wealth to non-coin assets such as land or art.)
Infographic summarizing Roman currency debas*m*nt - Note the graphic "Silver content of an individual denarius" - debas*m*nt occurred repeatedly and frequently. There was no single event.