First off the city "Byzantium" was replaced by the Emperor Constantine in the 4th century. There was never a "Byzantine" empire.
Second The Roman Empire was the longest lasting european empire in history with probably the largest impact on the western world.
Third The Eastern Empire was the economic, cultural, social, and military center of the greater roman world. I have no idea why the w*st*rn empire agreed to that particular division. Gaul, Iberia, Numidia, Britain, and Germany are all terrrible provinces and Italy by itself is nothing compared to Egypt, Greece, and Annatolia.
Fourth the Roman Emperor upheld Christianity, and the western way of life for over a thousand years until the dark times...until the pope worshiping backstabbers sacked the city during the 4th (((crusade)))
Fifth it is your solemn duty, as a student of history and a steward of grand strategy, to safeguard the true Empire of Christ on Earth. To restore His Holy Empire to it's rightful place as King of the Christian Kings, and to destroy the unwashed hordes of pagans and put down the heretical mudslimes once and for all.
Go forth Basileu, strike down the pompous and ambition roman pontifex, suppress the independant barbarian "kings" of europe, destroy the nomadic savages of the north, rescue the land of Christ from the sword of Islam, end the endless hordes of the east, and return the world to Peace, and Justice under your righteous rule.