Diocletian

Two dates, three days apart

The accepted date for Diocles's formal accession is 20 November 284, three days after this entry's listed date. Diocles, commander of Numerian's imperial guard, was declared emperor by the eastern army near Nicomedia.

One reconstruction, in the Claremont Coptic Encyclopedia, splits the difference: an initial selection and the killing of the praetorian prefect Aper on 17 November, formal proclamation three days later. Stronger chronological evidence supports 20 November as the official dies imperii.

A much later text, the Chronicon Paschale, gives September dates and puts the event at Chalcedon. Its modern editors reject that chronology in favor of 20 November at Nicomedia.

An emperor with a living rival

Numerian's death had been concealed — his body reportedly discovered in a curtained litter during the army's return from Persia — leaving the returning force without an emperor and pushing its officers into an assembly.

Eutropius reports that at the army's first assembly Diocles swore he had not plotted Numerian's death, accused the praetorian prefect Aper of the killing, and killed him with a sword before the assembled soldiers. The surviving narratives are brief and partisan, and their accusation against Aper is not independent proof of his guilt.

What the assembly produced was not a sole ruler of the Roman Empire: Carus's surviving son Carinus remained emperor in the West, and stayed Diocletian's living dynastic rival until 285.

The name came later too

The man acclaimed that November was Diocles. Documentary evidence from Egypt still recognized him under that name on 7 March 285, before the form Diocletianus became standard.