This type of presentation on the reverse is relatively rare during the Roman Empire. The appearance of Mercury is probably related to the plague epidemic that ravaged the Empire in 250-251 AD and of which Hostilian, Herennius brother died.
Roman Imperial
Herennius Etruscus (son of Trajan Decius), Antoninianus 250-251, mint of Rome
Obverse: radiate bust of the emperor right
Q HER ETR MES DECIVS NOB C
Reverse: Mercury with caduceus and purse standing left
PIETAS AVGG
Weight 2,81 g.
