Quo Vadis by Henryk Sienkiewicz
This novel tells the story of a young couple that falls in love in Rome, during the time of Nero. With their story as the main thread, it explores the decadent life of the Augustans and Caesar in Rome and the drastically different life proposed by the early Christians. It can be slow at times for modern readers as many of the arguments against the faith of Christ are proposed by philosophers of Rome within the text. For the same reason, it is a powerful record of the revolutionary ideas within the Christian faith, ideas that led early Christians to be nearly incomprehensible to the Romans, and yet indescribably attractive for many.
Peter and Paul are both important characters in the book. Peter's legendary encounter with Christ as he flees Rome is the source of the title. It means "Where are you going?" Peter asks the question of Christ who replies that he is going to Rome to be crucified (again). Peter immediately turns around to face his own eventual execution. It is, of course, a question we should all ask ourselves.
As a warning, this book is only for mature readers. The scenes of Roman life include all of its immorality. Also, after the great fire, the torture and slaughter of Christians in the Games is described in detail. I found myself weeping as I read those parts and even had to stop a few times. The martyrs of the early Church should not be forgotten, but their deaths were indeed horrible.
I read the version linked above, translated by W. S. Kuniczak, available at our library, but I noticed there is a translation available to read for free on the Kindle.