Final answer:
Constantine the Great and his son Constantius maintained orthodox Christian beliefs and fought against heresies, bolstering the position of bishops and entwining Christianity with the Roman state apparatus. The significant event during Constantine's reign was the Council of Nicaea, which affirmed Christ's divinity, shaping Christian orthodoxy.
Step-by-step explanation:
Constantine the Great and his son Constantius were pivotal figures in establishing Christianity as the dominant religion in the Roman Empire, and much of their efforts were spent in fighting heresies and developing an orthodox Christian belief system. Constantine's reign as sole emperor was marked by a conservative approach, with his conversion to Christianity geared towards the preservation and continuation of the Empire. This conversion also significantly increased the secular power of bishops, putting them on par with Roman nobility in terms of influence within the political system.
In 325, Constantine convened the first ecumenical council, the Council of Nicaea, aiming to resolve the controversies surrounding Christ's divine nature. The outcome of the Council was the Nicene Creed which declared Jesus to be 'consubstantial' with God, affirming his divinity and establishing it as orthodox belief. The subsequent emperors, following Constantine's lead, also worked closely with the bishops to promote Christianity across the empire, legislating against pagan practices and shaping the role of the state church.
Interestingly, not all of Constantine's successors followed his religious policy to the letter. For example, his son Constantine V became an iconoclast, rejecting the use of religious images. The predominant thread, however, was that Constantine and his dynasty, except for Julian's brief attempt at pagan revival, were ardent promoters of Christian orthodoxy.