Early Christianity developed within the Roman Empire in the first centuries CE. It grew out of Judaism and the teachings of Jesus and his apostles. Christianity initially spread among Jews but then the apostles, especially Paul, helped spread it throughout the Roman Empire. While Christians faced periods of persecution from Roman authorities who saw the new religion as a threat, Christianity continued to grow rapidly. By the 4th century CE, Constantine declared Christianity the official religion of the Roman Empire, leading to its eventual dominance in the Western world.