Diocletian separated and enlarged the empire's civil and military services and reorganized the empire's provincial divisions, establishing the largest and most bureaucratic government in the history of the empire.
Diocles' parents were of low status, and writers critical of him claimed that his father was a scribe or a freedman of the senator Anullinus, or even that Diocles was a freedman himself.
The first forty years of his life are mostly obscure.
Born to a family of low status in Dalmatia (Roman province), Diocletian rose through the ranks of the military to become roman cavalry commander to the Emperor Carus.
After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor.
On 20 November 284, the army of the east gathered on a hill 5 kilometres (3.1 mi) outside Nicomedia.