Diadumenian was born on 14 September 208, named Marcus Opellius Diadumenianus, to
Macrinus, the
praetorian prefect and future emperor of
Berber origin. The unreliable , a collection of
biographies of Roman emperors and usurpers, mistakenly names Diadumenian as "Diadumenus". The same source also states that Diadumenian's mother (Macrinus' wife) was called
Nonia Celsa, though this name may have been invented by the author of the text. Little information survives about Diadumenian, although the details of his physical appearance can be deduced from coinage and a description from the , which relates that he was "beautiful beyond all others, somewhat tall of stature, with golden hair, black eyes and an aquiline nose; his chin was wholly lovely in its molding, his mouth designed for a kiss, and he was by nature strong and by training graceful". Having served as praetorian prefect under
Caracalla, Macrinus participated in a plot to have the Emperor assassinated and exploited the resulting power vacuum to seize the throne for himself on 11 April 217, three days after Caracalla's death. Shortly after, the eight-year-old Diadumenian was elevated to formalising his position as heir to the throneat
Zeugma, while his guard was escorting him from
Antioch to
Mesopotamia to join his father. He was also given the name Antoninus, in honour of the
Antonine dynasty, at this time. On 16 May 218 a revolt against him and his father was launched in
Emesa by
Elagabalus, whose mother,
Julia Soaemias, was Caracalla's cousin. In order to put down the revolt, Macrinus led his legions to a fort at
Apamea. There Macrinus elevated Diadumenian to , making him co-emperor. After Macrinus was defeated by Elagabalus on 8 June 218, at the
Battle of Antioch, Macrinus fled north and then to the
Bosporus. Before fleeing, he entrusted Diadumenian to loyal servants, instructing them to take him into the
Parthian Empire, to the court of
Artabanus IV, to ensure his safety. Diadumenian was captured en route in Zeugma and executed in late June. His head was brought to Elagabalus and reportedly kept as a trophy. Following the demise of both Macrinus and Diadumenian, the
Roman Senate quickly proclaimed their support for Elagabalus, declaring the former emperors to be enemies of the state. They were subject to a process known in modern scholarship as , with their images and mentions in inscriptions and
papyri being destroyed during the reign of Elagabalus. In an attempt to wipe out all traces of Diadumenian and his father, Elagabalus dated his own reign to the end of that of Caracalla. Surviving busts of Diadumenian are mangled, with the facial features barely being discernible. ==Numismatics==