In spite of these failures and challenges, Diocletian's reforms fundamentally changed the structure of Roman imperial government and helped stabilize the empire economically and militarily, enabling the empire to remain essentially intact for another 150 years despite being near the brink of collapse in Diocletian's youth.
Carinus quickly made his way to Rome from his post in Gaul as imperial commissioner and arrived there by January 284, becoming legitimate Emperor in the West. The Sassanid king Bahram II could not field an army against them as he was still struggling to establish his authority.
By March 284, Numerian had only reached Emesa (Homs) in Syria; by November, only Asia Minor.
The first time Diocletian's whereabouts are accurately established, in 282, he was made by the newly Emperor Carus commander of the Protectores domestici, the élite cavalry force directly attached to the Imperial household – a post that earned him the honor of a consulship in 283.
– left his sons Numerian and Carinus as the new Augusti.
Although effective while he ruled, Diocletian's tetrarchic system collapsed after his abdication under the competing dynastic claims of Maxentius and Constantine, sons of Maximian and Constantius respectively.
The Diocletianic Persecution (303–11), the empire's last, largest, and bloodiest official persecution of Christianity, failed to eliminate Christianity in the empire; indeed, after 324, Christianity became the empire's preferred religion under its first Christian emperor, Constantine.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.He established new administrative centres in Nicomedia, Mediolanum, Sirmium, and Trier, closer to the empire's frontiers than the traditional capital at Rome.Julianus minted coins from the mint at Siscia (Sisak, Croatia) declaring himself as emperor and promising freedom.It was all good publicity for Diocletian, and it aided in his portrayal of Carinus as a cruel and oppressive tyrant.He defeated the Sarmatians and Carpi during several campaigns between 285 and 299, the Alamanni in 288, and usurpers in Egypt between 297 and 298.