mgcoins database

Antioch AD 293-294 billon antoninianus 3.81 g 2.04 cm 2.04 cm 1h

obverse: hd Diocletianus r radiate, draped and cuirassed IMP C C VAL DIOCLETIANVS P F AVG
reverse: Diocletianus and Jupiter holding sceptre, donating the emperor Victory on globe CONCORDIA MILITVM, I, in ex .XXI
RCV III 12339
Holleman munten List 94, *176, March 1993 

Gaius Aurelius Valerius Diocletianus c 245 284-305 c 313 (Split)

Officina mark I (=10) on reverse
'XXI' mark perhaps indication of silver content
273 Aurelianus restored the antoninianus to about its original size and fixed the silver content at about 5%
294 starting of a radical reform of the coinage
two new denominations: siliqua (argenteus) fineness and weight as the reformed Neronean denarius
follis, a large billon coin containing 5% silver
antoninianus discontinued
till about 304 post-reform radiates without the XXI mark, contained no trace of silver