Book I: Chapter i -- Who Were the Pissed-Off Pagans?

Augustine's opening argument against the pagans depends upon two historical claims which may be difficult to verify:

1. that when Alaric's Goths sacked Rome in 410, they spared Romans who had taken refuge in Christian places of worship; and 
2. that afterward, the pagan Romans who had been thus spared blamed the misfortunes of their city upon the Empire's move from paganism to Christianity.

The first claim seems probable.  The Goths were themselves Christians.  Their conversion is said to have begun after 238, when their raiders took many Roman captives, notably women, who were already Christians.  Although there was conflict between Christian and pagan Goths throughout the fourth century, a Gothic bishop appears to have been present at the Council of Nicea, and Ulfilas translated the Bible into Gothic sometime in the middle of the century.  It would not be unnatural for these Christians, invading Rome, to show special mercy to Romans who sought sanctuary in Christian churches.

In addition to Augustine, both his friend and collaborator Orosius and his not-so-friendly contemporary Jerome say that this is what happened.  (Of course, neither of them was there at the time, so they would only have heard the same stories Augustine had -- in Orosius's case, from the same people).  Moreover, although Augustine does not seem to know it, there were precedents in Greco-Roman military history.  Both Alexander (at Tyre) and Agesilaus (at Coronea) had spared people who took refuge in various temples temples.

But there are reasons to wonder.  For starters, the Goths were Arian and the Romans were predominantly Catholic -- meaning that their forms of Christianity differed not only in doctrine but in hierarchy.  Nor were they on friendly terms.  After Nicea, the bishops of each group had excommunicated each other, and refused to recognize each other's authority or jurisdiction. Their competition was often rough, and sometimes grew bloody.  So it is just as natural to imagine that, when Romans took refuge in Catholic churches, their Arian enemies would have massacred them on religious grounds.

On top of that, the Goths were not entirely part of Greco-Roman culture.  Although Gothic warriors had, at times, served in the Roman army, they were part of a different society.  Augustine does not identify them as Christians (which would not necessarily undermine his argument about theodicy), but calls them barbari.  Even though they share his faith, in most regards, they are cultural outsiders, strangers to him in a way that the pagan Romans are not.  I have no idea what role mercy toward defeated enemies may have played in their military culture.

As to the second claim, well, it is hard to say.  Were there, in fact, pagan refugees from Rome -- the same ones who had, according to Augustine, sheltered themselves in Christian churches -- who now blamed Christianity for the fall of their city?

It would not be surprising if there were.  Their city had, in point of fact, been attacked by Christians of the Arian persuasion.  But that is not the claim that Augustine attributes to them; he says, rather, that they blamed the Roman Christians, the ones who had been attacked along side themselves, for contributing to Rome's spiritual decay.

If such claims were made in writing, I do not know about it.  That's no surprise; I'm no classicist to begin with, and in any case vast amounts of pagan literature are now lost to us, sometimes through the vagaries of time and sometimes through deliberate destruction by Christians or, later, Muslims.  Still, Origen's rebuttal of the gnostic Celsus managed not only to name the guy but to preserve big portions of his argument; it would be helpful if Augustine had performed a similar service to his opponents -- and the fact that he did not raises my eyebrow a little.

A related question is just how many active pagans remained in the city of Rome at the time of Alaric's attack in 410.  This was almost a full century after Constantine declared Christianity a religio licita within the empire, and promptly began to offer it a variety of special privileges -- tax exemptions, unused government buildings (basilicae) and subsidies -- as well as placing inhibitions upon pagan practice, such as a ban on blood-sacrifice.  From the 380s forward, an increasingly Christian society had clamped down even harder on the remaining pagans.  Theodosius, who from 392 became the last emperor to rule both East and West, closed temples all through the empire, but also took a variety of strong anti-pagan steps in Rome itself:  people were forbidden to visit the temples or "raise their eyes" to the statues of their old gods; the flame in the Temple of Vesta was put out, an appeal to return the Ara Pacis to its former place was rejected, haruspicy and similar practices were (again) forbidden.  Violators forfeited their house, which may suggest that these restrictions were aimed especially at the wealthier classes.

For what it's worth, Theodosius took many of these steps under the heavy influence of Ambrose of Milan -- the bishop whose presentation of the Gospel had so moved Augustine years earlier.

It is clear that paganism endured in rural areas and far from the Eternal City.  But in Rome, its central practices had been illegal for a generation by the time Alaric attacked.  This does not mean, of course, that the laws were followed, nor that they were loved even by those who did follow them; there seems to be no agreement among historians about that.

The timing suggests two things:  first, that the number of pagans among the refugees may have been comparatively small, and they were under great legal pressure to keep quiet about their religious preferences; and second, that if there were any pagans left, they were likely to be pissed off.  In the course of a century, they had been discriminated against with increasing fervor.  Their relatively tolerant regime of worshipping any gods at all, so long as you were pious about it, had been legislated out of existence, and replaced with an authoritarian system under which one God was to be recognized - a system enforced by imperial official working hand in glove with the leaders of the upstart religion.

So Augustine's claim at the outset is likely to be true -- pagans may well have complained that Christianity had somehow left Rome open to defeat.  But if so, we should remember that (a) Rome was defeated by other Christians; (b) the number of pagans making such a claim is likely to have been very small; and (c) Augustine doesn't identify any particular people making the claim.  This leaves open the possibility that Augustine is responding to some very minor claims, the bitching and moaning of a few displaced persons, rather than a major philosophical movement -- and even the possibility (however remote) that Augustine has made the complaint up, constructing a straw man for the exercise in apologetics he has planned.