Ancient Rome
Judaism was common in the ancient Roman world, and there was a Jewish diaspora in many cities like Rome from the Hellenistic period. Christianity started in the east in Hellenistic Judaea. In Classical Antiquity, the Roman government did not like Christianity. Sometimes, Roman governors or emperors ordered the persecution of Christians. Under Emperor Diocletian, the persecution became the strongest. Christianity became an officially-supported religion in the Roman Empire under Constantine I. With the signing of the Edict of Milan by Licinius and Constantine in 313, it became the most powerful religion, and the Christian Church began the persecution of Christians with whom the official ("orthodox" and "catholic") disagreed. Then, in 391 AD, an edict of Theodosius I made Christianity Rome's official religion. The state church of the Roman Empire became the state religion in the empire. (The state church later split into the modern Orthodox Church and the Roman Catholic Church.)