Why was the Roman world eventually Christianized?

One important reason for the spread of Christianity was
the evangelical missions of Paul of Tarsus.  Paul, originally called Saul, was perhaps
the one person most responsible for the spread of Christianity throughout the Roman
Empire.  Paul was not one of the original 12 Apostles of Jesus Christ, whose life and
teachings are the basis of the Christian religion.  Paul originally persecuted the
followers of the teachings of Jesus until he had a conversion experience after which he
became a strong follower of Christ and began his evangelical missions.  Paul, a Greek
speaking Jew from Asia Minor, went on three missions covering 10,000 miles over the
course of thirty years.  He traveled through Palestine, Syria, Asia Minor, Macedonia,
Greece, and Rome, establishing Christian communities in each area. Paul made the
decision to spread the Christian faith to non-Jews, which helped establish the Christian
religion throughout the Roman Empire. The Roman system of roads allowed the Christian
message to travel quickly from one place to another.  The fact that Paul spoke Greek and
was a Roman citizen also helped Paul in his travels to spread the Christian
religion.