Antoninianus

Introduced by Caracalla in AD 215 and worth two denarii, the antoninianus is recognisable by the emperor's radiate crown (vs the laurel wreath on the denarius). As Rome's financial crisis deepened, its silver content plummeted from around 50% to almost nothing by the 260s AD — a tiny disc of bronze with a silver wash that fooled nobody. Its collapse triggered Diocletian's currency reform.