Greek-speaking communities of the Hellenized East were instrumental in the spread of early Christianity in the 2nd and 3rd centuries, and Christianity's early leaders and writers (notably St Paul) were mostly Greek-speaking, though generally not from Greece itself. The New Testament was written in Greek, and some of its sections (Corinthians, Thessalonians, Philippians, Revelation of St. John of Patmos) attest to the importance of churches in Greece in early Christianity. Nevertheless, much of Greece clung tenaciously to paganism, and ancient Greek religious practices were still in vogue in the late 4th century AD, when they were outlawed by the Roman emperor Theodosius I in 391-392. The last recorded Olympic games were held in 393, and many temples were destroyed or damaged in the century that followed. In Athens and rural areas, paganism is attested well into the sixth century AD and even later. The closure of the Neoplatonic Academy of Athens by the emperor Justinian in 529 is considered by many to mark the end of antiquity, although there is evidence that the Academy continued its activities for some time after that. Some remote areas such as the southeastern Peloponnese remained pagan until well into the 10th century AD.

In what language was the first book of the Bible conceived?