As previously noted (The Bones of Pagan History and Pagan Identity, Part One), there are two diametrically opposed views of the relationship between ancient and modern Paganism. One position rests solidly (or, perhaps one should say, rigidly) on an absolute denial of any survival of ancient Paganism, so that there is simply no possibility that modern Paganism could be in any manner connected with the Paganism of the past. In extreme cases this viewpoiont finds expression in the accusation that all notions of any connection whatsoever between modern Paganism and ancient Paganism amounts to "the trap of fundamentalism".
The other position accepts that ancient Paganism did, at least in some sense, survive, so that modern Paganism can reasonably be allotted some amount of historical rootedness. This category is fairly broad and could, conceivably, include those who might actually deserve to be labeled as "fundamentalists" for claiming, for example, that modern Wicca is the modern expression of an unbroken lineage that has preserved intact and unchanged some religious cult dating back to the Stone Age. One small problem is that such "fundamentalists" simply do not exist, but perhaps we should not allow ourselves to be distracted by anything so trivial as mere facts! On the other hand, there are a great many modern Pagans (almost certainly the vast majority) who do conceive of themselves as the modern-day inheritors and continuators of ancient religious traditions, but without going (anywhere near) so far as to claim that these traditions have remained unchanged through the centuries. In most cases, modern Pagans readily accept, as did Gerald Gardner, that our present day Pagan beliefs and practices represent a mixture of traditions from a variety of cultures and historical periods, including a non-negligible amount of quite recent additions.
However, the whole matter of ancient Paganism's survival can also be profitably studied in it's own right, without necessarily being concerned about any possible connection between ancient and modern Paganisms. This approach more narrowly focuses our attention on the fourth century AD (and the next century or two or three before and after), posing the question of whether or not during this period ancient Paganism "died".
(More broadly speaking, Christianization is not, of course, at all strictly limited to the religious transformation of the Roman world during late antiquity. But to the extent that one wishes to investigate the whole historical process Christianization in the broadest possible sense, then one's first order of business still has to be understanding the Christianization of the Roman world.)
If one focuses on the rise of Christianity in late antiquity, and the concomitant decline of Paganism, this leads to two subsidiary questions depending on how one answers the question: did Paganism die? If the answer is "yes", then one must futher inquire into manner of the death of Paganism. Alternatively, if Paganism somehow survived, then it must be asked: what was the nature and mode of this survival?
There are at least five distinct kinds of answers to the question of whether or not Paganism died:
1. Paganism died a violent death. This means both (1) that Paganism was actively suppressed by Christians, and (2) that Pagans actively resisted this suppression.
Sources supporting this view: MacMullen, Brown, Trombley, Chuvin, Hedrick, Zagorin, Bury, Gibbon
2. Paganism died a peaceful death because by the time Christianity came along, Paganism was already moribund and very close to dead anyway. Therefore it was not necessary for Christians to apply much, if any, pressure on Pagans, nor were Pagans in any real position to offer any resistance.
Source supporting this view: Alan Cameron
3. Paganism did not really die, so much as it gradually transformed itself into Christianity, by way of the missing link of "Pagan Monotheism". This point of view, like the one above, claims that the transition from Paganism to Christianity was largely peacefully, and even, in the words of Stephen Mitchell, "tidy".
Sources: Mitchel & Co. (the whole motley "Pagan monotheism" gang)
4. Paganism did not die but rather went underground. In this case it is posited that there existed crypto-Pagans who practiced dissumulation, that is, they publicly professed to be Christians while secretly and self-consciously rejecting Christianity and continuing to practice the "Old Religion", so to speak.
Sources supporting this view: Anthony Kaldellis, Niketas Siniossoglou
5. Paganism did not really die, but after a certain point there were no longer any people that could any longer be accurately called Pagans. In this case it is posited that while Pagan beliefs and practices were kept alive, the agents of this "survival" were people who were sincere, if possibly heterodox, Christians.
Source supporting this : Ronald Hutton in chapters 4 and 5 of his Witches, Druids and King Arthur.
One thing cannot be doubted. To the extent that there were any Pagans who wholeheartedly resisted conversion to Christianity, then it must undeniably be the case that there was a period of time when these Pagan diehards stubbornly continued to worship the old Gods even after all public forms of Pagan religious practice had become impossible. So the real question is whether or not there was any such formidable resistance to Christianity, for as long as there was such resistance, Paganism was still very much alive. And this, of course, is not an open question at all, but rather one to which, at least in terms of the basic facts, the answer is clearly established beyond any reasonable doubt. We know that such wholehearted resistance absolutely existed and that, furthermore, it was not limited to any one social class or group or to any one part of the Empire. We know that there was such resistance in the ancient city of Rome itself, and also that Athens was another center of resistance. But we also know that there was determined resistance to Christianization in such far flung parts of the Empire as Britania, Egypt and Anatolia.
We also know that in the 8th century the Saxons had their turn to fiercely resist conversion by the sword at the hands of the Franks. We also know that the Saxons were far from alone, and that Frisia, Denmark, Norway and Iceland were also centers of resistance. We know that the Baltic peoples continued to resist even in the face of the Northern Crusades, which lasted for over two centuries. Baltic Pagans even succeeded in establishing a powerful Pagan Empire in the heart of northeastern Europe that lasted well into the 14th century!
And even after Europe was finally "Christianized", the same kind of fierce resistance is seen in the Americas, Africa, Asia, and Oceania, and this resistance is ongoing today in the 21st century. But then we have come full circle, back to the question of the relationship between modern and ancient Paganism. If we stupidly reduce Paganism to an epiphenomenon that exists only as a kind of appendage to isolated, disconnected, mutually exclusive "cultures" or, worse, "ethnicities", then we have already surrendered ourselves to the Christian strategy of divide and conquer.
Modern Pagans only deserve to consider ourselves Pagan if we unhesitatingly embrace everyone who has ever cursed the name of Christ and sworn to go down fighting rather than meekly submit to the missionaries, and prayed to the Gods for the chance to take as many Christians as possible with them in the process. And we only deserve to call ourselves Pagan if we unhesitatingly embrace as our spiritual kin those who chose more subtle modes of resistance, keeping the worship of the Gods alive in secret from generation to generation.
In sum, both Pagan history and Pagan identity are inseparable from the historical question of Pagan resistance. Those who either deny that such resistance has taken place and continues to take place, or who seek to diminish the importance or extent of this resistance, or who decline to identity with and declare solidarity with those who have engaged in this resistance, cannot in any sense be considered Pagans.