huh? emperors regularly debased the currency; that’s inflation by another name. same effect
On the other hand, a fiat currency issuer doubling the money supply can (not necessarily will![1]) indeed reduce the value of any fiat I hold.
And incidentally coin debasement in the late Empire was largely due to the empire's economy and thus need for currency growing and exceeding the available supply of precious metals. If only they'd had double-entry bookkeeping...
[1] This is because money can't cause inflation, ie drive up prices, unless it's actually used to bid them up.
There has been a historical case of actual monetary inflation in a commodity based currency system and that was in Spain. The treasure fleets brought back so much gold that there really was too much money chasing too few goods and services. It should be obvious that that kind of inflation is operationally a very different thing than currency debasement and much closer to issuing new fiat.