Saint Constantine, also known as Constantine the Great, was a Roman emperor who ruled from 306 to 337 AD. He is best known for being the first Roman emperor to convert to Christianity and for issuing the Edict of Milan in 313 AD, which granted religious tolerance throughout the empire. His reign marked a significant turning point in the history of Christianity, as it transitioned from a persecuted faith to one that was embraced by the state. Constantine also played a crucial role in the establishment of Constantinople (modern-day Istanbul) as the new capital of the Roman Empire in 330 AD. This city became a major center for trade, culture, and Christianity in the centuries that followed. Saint Constantine is venerated as a saint in both the Eastern Orthodox Church and the Roman Catholic Church, and his legacy continues to influence religious and political thought today.