Numerian died in 284.

Prior to Diocletian's accession to power, the Roman Empire was ruled by a co-emperorship with Carinus in charge of the east and Numerian, his younger brother, in charge of the west. Diocletian was proclaimed emperor when Numerian died. Carinus set out to fight Diocletian, but lost.

The Empire was turbulent - two Emperors ruled together from 286 AD, Diocletian and Maximian. This is after an Emperor had died, Numerian, and war broke out between his successor Carinus and Diocletian.

The number of provinces of the Roman Empire varied over time. Under the Republic there number of provinces reached 15. Under the period of the Principate (from the rule of Augustus to that of Numerian, 27 BC to 284 AD) the number had reached 39. Emperor Diocletian (ruled 285-305 AD) increased the number to 122 by subdividing the existing provinces. Constantine the great (ruled 324 to 337 AD) reduced thenumberslightly. There were also changes in the structure and number of the provinces in the late Empire.

Ancient Rome had more than one type of government over the 1,200 years of her history. The first form of government was the monarchy which lasted 244 years (753 BC-509 BC). This was followed by the republic which lasted for 482 years (509 BC-27 BC). Then there was rule by the emperors. Historians divide this into two periods: the principate (from the reign of emperor Augustus to that of Numerian, 27 BC to 284 BC) which was a period of benign rule by the absolute rulers and the dominate (from the reign of Diocletian onward) when emperors became more autocratic rulers.