In what century and into what parts was the Roman Empire divided?

This happened in 395, i.e. in the 4th century. Theodosius bequeathed the western part of the empire to Flavius, his eldest son, and the eastern part to his brother Honorius. The Western Roman Empire did not even exist for a century, but the Eastern, known to us as Byzantium, fell only in 1453, after the capture of Constantinople by the Turks. Whether the division can be called a geopolitical catastrophe or, on the contrary, a very wise move by Theodosius I, which allowed to extend the existence of the eastern part of the formerly united state by more than a thousand years, continues to be a controversial issue.