Silver antoninianus, 22mm, 5.37gm, issued AD 215. Rome mint.
Obv: ANTONINVS PIVS AVG, Radiate, draped bust facing right.
Rev: PM TRP XVIII COS IIII PP, Sarapis standing holding right hand and sceptre in left.
What we now call the antoninianus was introduced by Caracalla in AD 215 as a double denarius, which depicted the emperor wearing a radiate crown. This new denomination was to last until Diocletian's reforms in the 290s.