As emperor of Spain, Gaul, and Britain, Constantine proved his strength against his barbarian enemies. However, when the other Roman emperors began to .\rbr\rbrAs emperor of Spain, Gaul, and Britain, Constantine proved his strength against his barbarian enemies. However, when the other Roman emperors began to .\rbr\rbrAs emperor of Spain, Gaul, and Britain, Constantine proved his strength against his barbarian enemies. However, when the other Roman emperors began to .\rbr\rbrRome: The Rise and Fall of an Empire - Episode 10: Constantine the Great (Documentary) The Roman Empire was the largest and most powerful in history, but .