Gaius Aurelius Valerius Diocletianus
AD284 ~ AD305
Gaius Aurelius Valerius Diocletianus was born in 245 to a common family and rose through the ranks of the army and when Carus was proclaimed emperor in 282 he set about gaining his trust. In 283 he was promoted to the rank of commander of the cavalry arm of the imperial bodyguard. Together with Carus, Numerian and Numerians' father in law Aper, they battled against the Sassanid empire and upon their victory plundered the Sassanid capital.
Once Carus died and Numerian became Augustus, it was Aper who claimed he was ill and that he ride back to Rome in a closed carriage. When the soldiers surrounding the carriage sensed a bad smell and discovered Numerian dead, Diocletianus accused Aper of killing Numerian and killed him personally. Diocletian was then elected Emperor by the troops in 284.
Soon after this election Carinus, the elder son of Carus, marched forward to fight for his right as lawful emperor but was quickly killed in battle.
By 298 he had intercepted Germanic and Sassanid invasions across the Danube, Rhine, Syria and Palestine.
During his rule he determined that by splitting the empire in two , it would become more manageable and prevent many of the problems that previous emperors had to face. He changed the structure of the Roman government ruling as an autocrat rather than a dictator and incorporated religion as well as military knowledge into his ruling.
The system was in place by 292 and Diocletianus took the eastern side of the empire and gave the western empire to Maximian with the imperial power divided between the two men and with two separate capitals while the senate remained in Rome.
In 293 each ruler appointed a Caesar to replace him, Galerius and Constantius were named and each of them as Caesar also automatically gained rule over a quarter of the empire.
In 305 both Diocletianus and Maximian retired although Diocletianus had the decision on his own and Maximian was persuaded to step down.