Constantine the Great is often recognized as the first Roman emperor to convert to Christianity, officially embracing the faith in the early 4th century. His conversion marked a significant turning point for Christianity within the Roman Empire, moving from a persecuted sect to a major religion. In 313 AD, he issued the Edict of Milan, which granted religious tolerance and allowed Christians to practice their faith openly. Constantine's support for the church included the construction of important basilicas and the convening of the First Council of Nicaea, shaping Christian doctrine. His reign fundamentally altered the religious landscape of Europe and laid foundations for the future of Christianity.