The Roman Emperor and the first Emperor of the age of Constantine. The third century AD was the darkest era of the ancient Roman Empire. Years of battles against the barbarians hollowed out the finance and undermined the prestige of the empire. The empire was torn apart by warlords and tottering towards extinction. In 306 AD, Constantine became the ruler of Rome, he had to struggle to survive under the difficult circumstance. After 20 years of relentless struggle, he finally defeated all enemies to unify the Roman Empire and became the only ruler of Rome. In 330 AD, Constantine the Great moved the capital from Rome to Byzantium. The history of Rome had turned to a new page since then and the new capital was renamed as Constantinople. In 313 AD, Constantine converted to Christianity. He not only changed the fate of the Roman Empire, but also at that moment, led Europe to enter the era of the Middle Ages.