mgcoins database

Antioch AD 293 AE antoninianus 4.08 g 2.18 cm 2.23 cm 6h

obverse: hd Diocletianus r radiate IMP C C VAL DIOCLETIANVS P F AVG
reverse: Diocletianus and Hercules donating the emperor, holding globe, Victory. XXI in ex, Z above IOV ET HERCV CONSER AVGG
RCV IV 12654
Munthandel G. Henzen list 242 (August 2012) no. 673 

Diocletianus 244 284-305 311

Latin abbreviation: Iovio et Hercvlio Conservatori Augustorum - Jupiter and Hercules Protectors of the Emperors.
Diocletian, called himself Jovius, after Jupiter, and Maximianus, assumed the name of Herculius, after Hercules.

RCV IV 12654 Antioch 290-294 Jupiter and Hercules and not Diocletianus and Hercules
Officina mark Z (= 7)
273-294 XXI used to indicate billon with 5% silver ?