Answer:
Edict of Milan and acceptance of Christianity by Emperor Constantine the Great.
Explanation:
Edict of Milan is the condition which opened the way for Christianity throughout the empire while the empire declined. Edict of Milan is a proclamation issued by Emperor Constantine the Great in 313 AD. In this proclamation, permanent religious toleration for Christianity occur within the Roman Empire and after 10 years, it becomes the official language of Roman empire.
