At first, most Roman officials largely ignored the followers of Jesus, viewing them simply as one of the many splinter groups within Judaism, but slowly some came to oppose Christian practices and beliefs. They considered Christians to be subversive dissidents because they stopped practicing traditional rituals and they objected — often publicly or in writing — to the cult of the emperor. Some Romans thought that Christianity was one of the worst of the mystery cults, with immoral and indecent rituals. Pagans also feared that the Greco-Roman gods would withdraw their favor from the Roman Empire because of the Christian insistence that the pagan gods either did not exist or were evil spirits. And many worried that Christians were trying to destroy the Roman family with their insistence on a new type of kinship and pointed to Jesus’s words in the Gospels saying that salvation was far more important than family relationships.

Persecutions of Christians, including torture and executions, were organized by governors of Roman provinces and sometimes by the emperor, beginning with Nero. Most persecutions were local and sporadic in nature, however, and some of the gory stories about the martyrs are later inventions, designed to strengthen believers with accounts of earlier heroes. Responses to Christianity on the part of Roman emperors varied. Some left Christians in peace, while others ordered them to sacrifice to the emperor and the Roman gods or risk death.

By the second century Christianity was changing. The belief that Jesus was soon coming again gradually waned, and as the number of converts increased, permanent institutions were established instead of simple house churches. These included buildings and a hierarchy of officials often modeled on those of the Roman Empire. Bishops, officials with jurisdiction over a certain area, became especially important. They began to assert that they had the right to determine the correct interpretation of Christian teachings and to choose their successors.

Christianity also began to attract more highly educated individuals who developed complex theological interpretations of issues that were not clear in scripture. Often drawing on Greek philosophy and Roman legal traditions, they worked out understandings of such issues as how Jesus could be both divine and human and how God could be both a father and a son (and later a spirit as well, a Christian doctrine known as the Trinity). Bishops and theologians often modified teachings that seemed upsetting to Romans, such as Jesus’s harsh words about wealth and family ties. Given all these changes, Christianity became more formal in the second century, with power more centralized.