I was just speaking to a historian with an interesting take on the 'Christianity caused the decline and fall' hypothesis.
Essentially, they argued that the rise of the church actually usurped the secular social structures of the empire. The church acted as a source of authority distinct from that of empire. It managed to remain vibrant, wealthy and expanding whilst the empire experienced economic (inflation, unsteady sources of taxation etc) and martial difficulties.
One important result of this was that the church provided an alternative route of advancement for men of ambition and talent. Such people sought to become priests, bishops and cardinals rather then generals, governors and administrators. The result left Rome with a shockingly small pool of high calibre leadership, and uniquely vulnerable to governmental upheaval. Essentially, it consigned the empire to maladministration.
Do you find this plausible?
Not really. For one thing, I have a hard time believing that the number of aristocratic persons who abandoned their wealth and avenue to government service to enter a life of celibacy and irrelevance in a monastery or in the Syrian desert was sufficiently high to limit the size of the Roman bureaucracy. The number of attested cases of this does not make up a significant cross-section of a ("the", I guess, since there's only one) late-Roman prosopography. Simply put, there's not enough hard evidence to support such a thesis.
At the same time Christianity was expanding and creating new bureaucratic structures and recruiting skilled managers for same, the Roman bureaucracy was
also expanding. The period between Constantinus I and, say, Valentinianus I (picked because of the famous Romanus Episode/"Leptisgate") saw the creation of a several thousand-man civilian bureaucracy that had not existed earlier in imperial history. If sources of effective managers were drying up due to tonsuring, one would not expect the secular bureaucracy to expand contemporarily.
And finally, the whole thing suffers from the issue of actually proving that it mattered. Not only would one have to indicate that at the very least, large numbers of aristocrats who were at least competent managers were entering the Church hierarchy instead of the secular bureaucracy, but also that the loss of these people caused an appreciable decline in tax efficiency and/or quality of governance, whatever the latter is supposed to be. I don't see a particularly high likelihood of unearthing something that would do that satisfactorily.
It's not really a new thesis. You can find a version of it in Gibbon, IIRC. One of the major uses Peter Heather's 2005 book has - other than as a paperweight - is a decent lecture-hall discussion of the issue of Christianity and bureaucracy. Shame that Heather couldn't put a
positive explanation into his book other than a rehash of the same tired old thesis he's been employing (with small variation) since 1990 or so.
I don't know that much about Roman and Byzantine history, but my understanding is that the Western Church was a more separate authority from the government then it was in the Eastern Church...
Dachs, tell me why I am horribly wrong!
You're not. The thing is, the Western Empire died before one can really say that caesaropapism really developed in the East. That's more of a sixth-century thing; comparing that with the fourth-century or fifth-century West would be silly.