Christianity becomes State Religion of Rome

With the Edict of Thessalonica in 380 AD, Emperor Theodosius I made Nicene Christianity the official state religion of the Roman Empire. This officially ended state support for traditional Roman paganism and Arianism. While it gave the Church unprecedented resources and influence, it also introduced new challenges regarding the relationship between Church and State. The Emperor's decree meant that being a Roman citizen increasingly meant being a Catholic, profoundly shaping the development of European civilization for the next thousand years.