It is obvious that Diadumenian's three main
types as
Caesar exactly correspond to Macrinus' three issues, which for their
part can be approximately dated on the basis of the titles they bear and their volumes of issue as revealed by the
Reka Devnia hoard. So Diadumenian's dates derive from those estimated for
Macrinus.
Dio Cassius tells us that
Diadumenian was named
Caesar and Prince of the
Youth by the Senate in May 217 as soon as news of Macrinus' accession reached
Rome. A little later, Dio continues, news arrived that
Diadumenian had independently been proclaimed
Caesar by the soldiers at Zeugma, as he was on
his way from
Antioch to join
Macrinus in
Mesopotamia, and that he
had also assumed Caracalla's name Antoninus. Hence
his first short issue of coins in
Rome with the titles
Caesar and Prince of the
Youth, but
still without Antoninus.
I treated all of these matters with full documentation and discussion in my paper on the coinage of
Macrinus, read at the 1979 International Numismatic Convention in
Bern and published in
Numismatische Zeitschrift 93, 1979.
