when did rome divided into east and west
Western Roman Empire Though the Empire had seen periods with more than one Emperor ruling jointly before, the view that it was impossible for a single emperor to govern the entire Empire was established by Emperor Diocletian following the disastrous civil wars and disintegrations of the Crisis of the 3rd century. His ideas were instituted in Roman law by the introduction of the Tetrarchy in AD 285, which divided the position of Augustus (Emperor) into two; one in the East and one in the West, each with an appointed Caesar (junior Emperor and designated successor). Though the tetrarchic system would collapse in a matter of years, the East-West geographical administrative division would endure in one form or another for centuries to come. As such, the Western Roman Empire would exist intermittently in several periods between the 3rd and 5th centuries. Though some emperors, such as Constantine I and Theodosius I, would manage to rise to the position of Augustus in both halves and as such reunify the Empire, it would often divide again upon their deaths. After the death of Theodosius I in AD 395, the Empire was divided between his sons after which it would never again be unified. Eighty-five years later, in 480, following various invasions and the collapse of central control in the West, Zeno of the Eastern Empire recognized the reality of the Western Empire's reduced domain—effective central control had ceased to exist even in the Italian Peninsula after the depositions of Julius Nepos and Romulus Augustulus—and therefore abolished the Western court and proclaimed himself the sole emperor of the Roman Empire.
Western Roman Empire Though Marcellinus does not refer to the Empire as a whole after 395, only referring specifically to its separate halves, he clearly identifies the term "Roman" as applying to the Empire as a whole. When using terms such as "us", "our generals" and "our emperor", Marcellinus distinguished both divisions of the Empire from outside foes such as the Sasanian Persians and the Huns.[139] This view is consistent with the knowledge that contemporary Romans of the fourth and fifth century continued to consider the Empire as a single unit, though more often than not with two rulers instead of one.[83] Though it was the first time the position was divided geographically, the concept of there being more than one emperor at a time was not unprecedented even before Diocletian and the Tetrarchy with there having been several periods where there were more than one co-emperor, such as with Caracalla and Geta 210-211 AD.[141]