The government had encouraged inhabitants, especially those in urban areas, to learn Greek, and the common language allowed ideas to be more easily expressed and understood.At first, Christians continued to worship alongside Jewish believers, which historians refer to as Jewish Christianity, but within twenty years of Jesus's death, Sunday was being regarded as the primary day of worship.In addition, the peculiar intimacy of Christian society and its secrecy about its religious practices spawned rumors that Christians were guilty of incest and cannibalism; the resulting persecutions, although usually local and sporadic, were a defining feature of Christian self-understanding until Christianity was legalized in the 4th century.A series of more centrally organized persecutions of Christians emerged in the late 3rd century, when emperors decreed that the Empire's military, political, and economic crises were caused by angry gods.The history of the Catholic Church begins with the teachings of Jesus Christ (c. AD 30), who lived in the Herodian Tetrarchy (later formed into the Roman province of Judea (Roman province) by the Roman Empire).

Christians' refusal to join pagan celebrations meant they were unable to participate in much of public life, which caused non-Christians–including government authorities–to fear that the Christians were angering the gods and thereby threatening the peace and prosperity of the Empire.

In 313, the struggles of the Early Church were lessened by the legalisation of Christianity by the Emperor Constantine I.

In 380, under Emperor Theodosius I, Catholicism became the state religion of the Roman Empire by the decree of the Emperor, which would persist until the fall of the Western Empire, and later, with the Eastern Roman Empire, until the Fall of Constantinople.

Rome could come to terms with the God of Hosts." When Constantine became emperor of the Western Roman Empire in 312, he attributed his victory to the Christian God.

Many soldiers in his army were Christians, and his army was his base of power.