Diocletian delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors, under himself and Maximian respectively.Under this 'tetrarchy', or "rule of four", each emperor would rule over a quarter-division of the empire.By March 284, Numerian had only reached Emesa (Homs) in Syria; by November, only Asia Minor.
Diocletian may have become involved in battles against the Quadi and Marcomanni immediately after the Battle of the Margus.
He established new administrative centres in Nicomedia, Mediolanum, Sirmium, and Trier, closer to the empire's frontiers than the traditional capital at Rome.
Building on third-century trends towards absolutism, he styled himself an autocrat, elevating himself above the empire's masses with imposing forms of court ceremonies and architecture.
His palace eventually became the core of the modern-day city of Split in Croatia.
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.
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.