The short answer is no. The slightly longer answer is definitely not. To be fair to this theory, which used to be very commonly accepted, most of the things that are attributed to the fall of Rome didn’t actually bring about the end of the Roman Empire. The idea that Christianity is responsible for the fall of Rome, to any extent, is largely not accepted anymore, but I have seen a few people who still believe it. Most of these people aren’t historians, or at least don’t study ancient history, and usually have something against either organized religion in general or Christianity specifically, and so they use it as a kind of scapegoat to say “see Christianity is definitely bad because it caused the collapse of the greatest empire in history.” This would be a ridiculous claim to make even if it were true that Christianity was responsible for the Roman Empire’s collapse, and it almost always seems to be made to support a biased argument.

As you might know, this theory originally gained popularity because of Edward Gibbon, who wrote that “As the happiness of a future life is the great object of religion, we may hear without surprise or scandal that the introduction, or at least the abuse of Christianity, had some influence on the decline and fall of the Roman empire. The clergy successfully preached the doctrines of patience and pusillanimity; the active virtues of society were discouraged; and the last remains of military spirit were buried in the cloister.” But to be fair to Gibbon he wasn’t completely negative in his views of Christianity as he also made the claim that Christaintiy tempered the ferocious nature of the Empire’s barbarian “conquerors”: “but the pure and genuine influence of Christianity may be traced in its beneficial, though imperfect, effects on the barbarian proselytes of the North. If the decline of the Roman empire was hastened by the conversion of Constantine, his victorious religion broke the violence of the fall, and mollified the ferocious temper of the conquerors.” Nevertheless, Gibbon’s views on Christianty were a product of the Age of Enlightenment, and he may have been directly influenced by men like Voltaire (though I only have a limited knowledge of this period so I can’t really say more about this). So it’s easy to see why Gibbon placed so much blame on Christianity, and why this view was able to gain such a foothold among historians who came after him, as many educated people were starting to question religion, particularly Catholicism.

But this is obviously a biased stance from Gibbon and other historians of the time, so we certainly can’t just take them at face value. Nor should you just take what I’ve written so far at face value, instead we must look at other sources, primarily we need to look at how the Romans themselves viewed Christianity during late antiquity. As with pretty much any topic from antiquity, but especially late antiquity, there is sadly a dearth of primary sources. Fortunately many of the histories written during the 4th century were written by members of the clergy and quite a few of these have survived to today, unfortunately the same can’t be said about the 5th century, at least not for the west. There are a good number of histories from the East from this period, or from subsequent centuries that covered the 5th century, but most primary sources for the western Roman Empire of late antiquity come from the 4th century (which make sense all things considered).

One source that does cover the early 5th century is Paulus Orosius’ Historiae Adversus Paganos (Seven Books of History Against the Pagans), which is a history of the Roman Empire but also an attempt to show how much better the world became because of Christianity. This book was also written in response to St. Augustine’s City of God, which is kind of a history but is mostly a philosophical work meant to show how Christianity was not responsible for the perceived decline of Roman civilization (namely in response to the sack of Rome in 410). I think these works are both very relevant to the question at hand, because the question was even being asked back then (albeit a little differently). Not only did Augustine and Orosius both set out to refute the idea that Christianty was responsible for the looming “collapse” of Roman society, but they also offer good insight into Christian thinking at this time. They, particularly Orosius, also show that Rome’s military was absolutely not weakened by the introduction of Christianty, one of the common arguments used to support this idea.

Since we’re on the topic of Orosius and Augustine, and the subtopic of Roman military strength, I want to start with the invasion of Radagaisus in 405-406. As Orosius tells us, Stillicho defeated Radagaisus, who probably had around 20,000 men, at the Battle of Faesualae with extreme ease:

“Indeed against that most cruel enemy, Radagaisus, it was granted that the minds of other enemies with their forces be inclined to give us aid. Uldin and Sarus, leaders of the Huns and of the Goths, were on hand to aid the Romans; but God did not allow the fact of His power to seem to be the valor of men and especially of the enemy. He forced Radagaisus, struck with divine terror, into the mountains of Fiesole…no army was drawn up for battle; no fury and no fear presented the uncertainties of battle; no slaughter was done; no blood was shed…therefore, King Radagaisus by himself, taking hope for escape, secretly deserted his men…moreover so great a number of Gothic captives is said to have been made that…they were sold for an aureus a piece. But God did not allow anything to survive of this people, for immediately…all who were bought died.” (Paulus Orosius, “Seven Books of History against the Pagans,” The Fathers of the Church vol. 50. 351-352.)

Now on the surface this reads less like a monumental Roman victory over an invading army and more like an act of divine intervention, but that’s because Orosius wanted it to be viewed that way (nor is it really the point right now). There was most certainly a battle of some kind at Faesulae, likely repeated attempts by Radagaiusus’ men to break past the Roman lines, with each of these failing as the Romans and their allies pushed the Goths back up the mountains. Eventually Radagaisus realized that he had no hope of getting his army out of the mountains and so he surrendered to Stillicho, who quickly had him executed, and roughly 12,000 of his men were captured. So the question we need to ask here is, if the Roman military was weakened by the introduction of Christianity why were they able to so easily defeat an army composed of devoted pagans led by a devoted pagan? And the answer to that question definitely isn’t divine intervention, its because the Roman military was still a formidable fighting force at this time and was more than capable of holding its own against Radagaisus’ army.