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.
He appointed fellow officer Maximian as Augustus, co-emperor, in 286.
Diocletian may have become involved in battles against the Quadi and Marcomanni immediately after the Battle of the Margus.
He eventually made his way to northern Italy and made an imperial government, but it is not known whether he visited the city of Rome at this time.
From at least 297 on, imperial taxation was standardized, made more equitable, and levied at generally higher rates.
Not all of Diocletian's plans were successful: the Edict on Maximum Prices (301), his attempt to curb inflation via price controls, was counterproductive and quickly ignored.
Augustus, the first Emperor, had nominally shared power with his colleagues, and more formal offices of Co-Emperor had existed from Marcus Aurelius on.
Most recently, Emperor Carus and his sons had ruled together, albeit unsuccessfully.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.Galerius, aided by Diocletian, campaigned successfully against Sassanid Persia, the empire's traditional enemy. Diocletian led the subsequent negotiations and achieved a lasting and favorable peace. Born to a family of low status in Dalmatia, 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.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.