Christianity underwent a transformation under Constantine, going from a minority religion that was persecuted to the main religion of the Roman Empire. Constantine issued the Edict of Milan in 313 CE, which provided Christians religious tolerance and formally acknowledged Christianity as a legitimate religion in the empire. He also had a significant impact on the Nicaean Council, which established many of Christianity's core beliefs, including the idea of the Holy Trinity.
In terms of Rome's fall in 476 C.E., it was a complicated process that occurred over several centuries and involved a mix of political, economic, and military elements. Since it signalled the end of Roman governmental dominance in Western Europe, the Western Roman Empire's final collapse in 476 C.E. is frequently considered as the symbolic culmination of this decline. However for several centuries after this time, the Eastern Roman Empire (Byzantine Empire) remained prosperous.