Ramsay MacMullen, Changes in the Roman Empire: Essays in the Ordinary
Princeton University Press, 1990), p. 150 with notes on p. 333:
Those standards were, to repeat, a great deal harsher in my period of study, A.D. 312 to 412, than in the preceding hundred years. Considering the whole span there covering two full centuries, is it possible to see anything in the nature or development of Christianity that might have helped produce the change toward harshness? The only evidence of that sort known to me, which is also the only sadistic literature I am aware of in the ancient world, is the developing Christian vision of Purgatory,45 surviving principally in apocryphal apocalypses and parts of the Sibylline Oracles. In the details abundantly provided in this literature depicting the torments of the wicked—hung up by their tongues, buried to their mouths in human excrement, their eyes put out with a red hot iron, and so forth—a connection is drawn between the elaborate infliction of pain and the will of God. Such a connection may have been found and felt likewise by the persecutors, earlier. In Diocletian's edict against the Manichaeans we sense it. He concludes several strident paragraphs with the statement, "We have established pains and penalties well deserved and suited to those people ... [who], together with their abominable scripture, are to be subject to a rather rigorous punishment: to be burned up in the fiery flames; and those who are of their allegiance, truly, and especially the more fanatical, we order to be beheaded."46 Observing both Christianity and an aroused paganism in operation, it appears to me likely that religious beliefs may have made judicial punishment specially aggressive, harsh, and ruthless. In both, the characteristics of action were similar, producing cruelty in the service of zeal. But there was also a major difference: pagan beliefs left daily morals to philosophy. For pagans, only correct cult mattered. Christian zeal in contrast was directed over all of daily life. Hence, threats and torture, the stake and the block, spread over many new categories of offense.
45. J. Le Goff, La naissance du Purgatoire (1981), draws principally on the Apocalypse of Peter and the Apocalypse of Paul, the first dating to the early second century, the second, to the mid-third (pp. 54 and 56); see W. Schneemelcher, New Testament Apocrypha 2 (1965) 664; tortures described in Apoc. Petri 7 (ibid. 672f., including mutilation, 716f.), compared with Or. Sibyll. 2.255-307.
46. FIRA2 p. 581 (Mos. et Rom. legum collatio 15.315-16).