Which event marked the establishment of Christianity as a dominant faith in the Roman Empire?

The Edict of Milan, issued in 313 CE, was pivotal in establishing Christianity as a major religion within the Roman Empire. By this decree, Emperor Constantine and his co-emperor Licinius legalized Christianity, granting religious tolerance and ending the persecution of Christians that had been prevalent prior to this time. The Edict allowed Christians to openly practice their faith and build churches, thus paving the way for Christianity to grow and solidify its influence within the empire.

This marked a significant turning point as it not only protected Christians but also set the stage for Christianity to eventually become the official state religion under Emperor Theodosius I in the late 4th century. The effects of the Edict of Milan extended far beyond its immediate impact, as it facilitated the spread of Christian doctrine, led to the church gaining power and wealth, and transitioned the focus of the Roman Empire toward a more Christian-centric political and cultural landscape.