History of the Roman Empire
Theodosius was the last Emperor who ruled over the whole Empire. After his death in 395, he gave the two halves of the Empire to his two sons Arcadius and Honorius; Arcadius became ruler in the East, with his capital in Constantinople, and Honorius became ruler in the West, with his capital in Milan and later Ravenna. The Roman state would continue to have two different emperors with different seats of power throughout the 5th century, though the Eastern Romans considered themselves to be the only ones who were fully Roman. Latin was used in official writings as much as, if not more than, Greek and the two halves were nominally, culturally and historically, if not politically, the same state.
History of the Roman Empire
As a matter of historical convention, the late Roman Empire emerged from the Roman Principate (the early Roman Empire), with the accession of Diocletian in 284, his reign marking the beginning of the Dominate, or Late Roman Empire. It may begin with the commencement of the reign of Diocletian in AD 284, following the Third Century Crisis of AD 235–284, and to end in the west with the collapse of the Western Empire in AD 476, while in the east its end is disputed, as either occurring at the close of the reign of Justinian I (AD 565) or of Heraclius (AD 641).