The reader is taken from the very first generation of Christians in Rome, a tiny group of Jews who acknowledged Jesus as the Messiah, down to the point when Christianity had triumphed over savage persecution and was on the verge of becoming the religion of the Roman Empire.
Rome was by far the biggest city in the Roman world and this had a profound effect on the way Christianity developed there. It became separate from Judaism at a very early date. The Roman Christians were the first to suffer savage persecution at the hands of Nero. Rome saw the greatest theological movements of the second century thrashing out the core doctrines of the Christian faith.
The emergence of the papacy and the building of the catacombs gave the Roman Church extraordinary influence and prestige in the third century, another time of cruel persecution. And it was in Rome that Constantine's patronage of the Christian faith was most evident as he built great basilicas and elevated the personal status of the Pope.