According to Church tradition, it was under Nero's persecution that the saints Peter and Paul became martyrs in Rome. Several of the New Testament writings mention persecutions and very difficult times. For 250 years there were times when Christians suffered from persecutions, because they refused to worship the Roman emperor. That was seen as treason and punished by execution. But the Christian religion continued to spread throughout the Mediterranean region. In the late fourth century they became the dominant religious force of the Roman Empire.