The Fall of the Western Roman Empire: An Archaeological and Historical Perspective is the latest book from Dr Neil Christie of the University of Leicester.
The division of the vast Roman Empire can be traced chiefly to the 280s AD when the Empire, wracked by civil wars and external threats across the Third Century, was firmly brought back under control. Nonetheless, the separation remained somewhat fluid until 395 when Theodosius I, the last ruler of a united Roman Empire, died leaving the two halves to his sons Arcadius and Honorius.
The Eastern Roman Empire subsequently flourished, spreading around the Mediterranean with its capital at Constantinople (today’s Istanbul). It peaked in the Sixth Century under the Emperor Justinian and persisted as the Byzantine Empire all the way through to the 15th century.
Click here to read this article from History of the Ancient World