In a large way, it was the greed of men like Calpurnius who assisted in the fall of the Roman Empire because they were jealous of Christianity and tired of the naturally principled life that the Romans led.
Quadratus confesses his Christianity the same time Sebastian does and is killed on the spot by one of his fellow soldiers.
Torquatus - a newly converted Christian. Torquatus begins by being overly zealous, but falls immediately when tempted. Fulvius sees right through him and knows exactly how to control him.
With Torquatus' help, Fulvius is able to make great strides toward his goal of assisting in the eradication of the Christians from the Empire.
Through Torquatus' betrayal, the pope, many of the priests and Caecilia are martyred.
At a later time in the story, Torquatus finds forgiveness and spends the rest of his life doing penance for his weakness during the persecutions.
Severus - Diogenes' son. Severus is a melancholy man like his father and takes everything very seriously. He helps their father dig the tombs of the cemetery.
Always a skeptic, it is Severus who sees Torquatus for what he is and is able to warn the others, but the harm is already done.
Emperor Maximian - "divine" emperor of the Western half of the Empire. A jealous man, Maximian views the Christians as a threat to his empire because he believes that their devotion to their religion competes with their devotion to Rome.
Accordingly, Maximian has launched a great persecution against the Christians where he enjoys watching them be tortured as well as in the arena against the wild beasts.
Maximian is described as, "Covetous to meanness, and spendthrift to recklessness, without restraint of any passion, without sense of justice, or feeling of humanity, this monster had never ceased to oppress, persecute, and slay whoever stood in his way.
Gigantic in frame, with the well-known features of his race (Serbian), with the hair on his head and face more yellow than red, shaggy and wild, like tufts of straw, with eyes restlessly rolling in a compound expression of suspicion, prolifigancy, and ferocity."
Coming in at the tail end of the fall of the Roman Empire, Maximian is the last emperor before Constantine arrives at the end of the mini-series.
Like all the pagans in Rome, he has heard enough lies about the Christians to think that they weaken the Empire, and he is happy to support their eradication from Rome.