The Roman Empire grew to be huge.
It covered most of Europe, North Africa, and parts of Asia. Just
getting messages from Rome to the outer parts of the Empire took
weeks. The Empire had become too large to rule
effectively. The outer provinces were pretty much doing what
ever they wanted
Emperor Diocletian was looking for a way to
fix this and other problems. He decided that the only thing to
do was to actually break the empire into two, a western empire one based in
Rome and an eastern one based in Byzantium. There would be two
emperors working together against outside enemies, but each ruling
their half separately.
This turned out to be a very good plan at
least for the Eastern half of the empire. When the Western Roman
empire collapsed, the Eastern Empire continued for another thousand