Denarius and Obolus

[Epictetus]

I’m curious about the early imperial currency system. As governor of Pontus and Bythnia, Pliny writes to Trajan about the Roman denarius as the common currency (Letter 113, among others). Yet about a generation later and close to the same area Lucian uses the Greek obolus (Alexander 19).

What was the relationship between the denarius and obolus during the Principate?

[Jona Lendering]

What was the relationship between the denarius and obolus during the Principate?

Weren't a drachm and a denarius equal? That means that the coin that Pliny, writing in Latin, calls a denarius, was called drachm by the "Graeculi" and subdivided into six obols.

[Epictetus]

Okay, so the denarius and drachma were two names for the same coin. Then would the obolus be called the as in the west? Would this be two names for the same coin?