Final answer:
Constantine played a critical role in Christianizing the Roman Empire, transitioning it from persecution to predominance. By converting to Christianity, issuing the Edict of Milan for religious toleration, and patronizing the Church, Constantine established the foundations of Christian governance in Rome.
Step-by-step explanation:
Emperor Constantine's role in the establishment of Christianity within the Roman Empire was instrumental. Under his reign from 306 to 337 AD, Christianity transitioned from a persecuted faith to a predominant religion. After his vision before the battle in 312 CE, Constantine's conversion promised victory through the Christian God. His formal conversion to Christianity is a well-accepted historical event that greatly influenced European and world history.
In 313, he issued the Edict of Milan, which granted religious toleration, marking a significant change for Christianity's role in the empire. Constantine became a great patron of the Church, and with imperial backing, Christianity began to intertwine with secular power, shaping the nature of religious practice and politics in Rome. Constantine's support led to the expansion of Christian institutions, empowering Christian officials, and ultimately the transformation of the Roman Empire into a Christian state. His family continued his legacy, further entrenching Christianity's place within the empire, thereby establishing the era of Roman Christian rule.