Diocletian Proclaimed Roman Emperor
The sudden death of Emperor Numerian during the army's return from a Persian campaign created another succession crisis in an empire weakened by decades of civil war and rapid changes of ruler. At a military assembly near Nicomedia on November 20, 284, senior officer Diocles was proclaimed emperor by the troops. He publicly accused the praetorian prefect Aper of murdering Numerian and killed him before the assembled army. Taking the imperial name Diocletian, the new ruler still had to defeat Numerian's brother Carinus before controlling the empire. His accession nevertheless marked the beginning of a more durable political settlement after the Crisis of the Third Century.
Why it matters: Diocletian reorganized imperial administration, taxation, provincial government, and military command, eventually sharing authority through the Tetrarchy. Although that system did not produce a permanent solution to succession, his reign transformed Roman government and laid much of the institutional foundation of the later Roman Empire and its more centralized style of rule.