Constantine refers to several historical figures, but most notably, it is often associated with Constantine the Great, a Roman Emperor who ruled from 306 to 337 AD. He is known for being the first Roman emperor to convert to Christianity and for establishing Constantinople (modern-day Istanbul) as the new capital of the Roman Empire. His reign marked a significant shift in the empire's religious landscape. Constantine played a crucial role in the spread of Christianity by convening the First Council of Nicaea in 325 AD, which aimed to address divisions within the church. His efforts helped to solidify the faith's position within the Roman Empire, leading to its eventual dominance in Europe.