Caracalla 198-217 - Antoninianus

4.99g

Obv: Radiate bust of Caracalla right "ANTONINVS PIVS AVG GERM"

Rev: Jupiter standing naked except for a cloak on his shoulder, holding a thunderbolt and staff "P M TR P XVIIII COS IIII P P"

RSC 338

Caracalla introduced the Antoninianus or Double denarius in 214AD (no one is sure of its real name).  It was tariffed at 2x a denarius.  The silver in it was more pure than that of a denarius (about 65% vs 40%) so it's weight is less than two times.  This was also called a "deceitful silver" at the time as the total silver content was still less than two standard denarii.  Basically it was still a debasement of the imperial coinage.   Minting of this coin was ended with Elagabalus only to be restarted again in 238 by Pupienus and Balbinus.