Constantine's role

the arch of constantine, rome

Theology is a subject I've tried to get into, and apparently Jason Rosenhouse and Jerry Coyne have been trying to do the same, with regard to modern theology. Being a lesser mortal, without immediate access to modern university material, and being too poor to be able to subscribe to scholarly journals, I've looked at whatever scraps came my way, such as the apparently dubious interpretations of Islamic theology offered up by Karen Armstrong, as well as more ancient theologies such as Augustine of Hippo's attempt to prove the existence of the soul, Anselm's ontological 'proof' of his god's existence, and historical interpretations of the thought of the likes of Origen and Arius.
Much of this I've found a real yawn, though I've occasionally been impressed by the ingeniousness, as well as the energy, of the arguments. I've tended to take the 'emperor's new clothes' position - is there really anything to talk about? This seems especially relevant to theology about Jesus - a person or a god or an aspect of a god? It seems to me that, before you start speculating about such things, you have to establish whether the guy ever really existed - a matter for empirical research, not pure intellectual speculation. But with theology in general, you have to have something of the other-wordly about you to appreciate it, and there's not much of that in me. And I find too little of the this-worldly in theologians.
To judge from Rosenhouse's experiences with modern theology [or theistic enquiry into the existence of gods, which isn't quite the same thing, but which is surely self-evidently problematic], I'm probably not missing much. From my reading, Rosenhouse thinks much like me on the subject - but probably with a greater command of formal logic - and once you encounter the first profoundly dubious or unwarranted assumption in these writings it's hard to find the energy or enthusiasm to go on. I'm more interested in the history of these debates, and their political implications, which aren't great these days, but were very great when the RCC ruled the roost, or when monarchs claimed to rule by divine right.
So I'm currently, through Robin Lane Fox, learning much about a key moment, probably the key moment, in the history of Christianity's relationship to secular authority, that's to say the Roman Emperor Constantine's accession to full power in 324, and his various decrees and speeches from that time, requiring the institution of Christianity as the religion of the emperor, if not of the state.
Constantine's conversion and its momentous impact has occasionally come up in conversations I've had with vaguely interested parties, and as always I've pretended to know more about the subject than I actually do. Now I can partially rectify the situation - I mean, I'll still pretend to know more than I do, but at least what I do know is a lot greater than before.
One issue Fox helps clarify is this: Wasn't it just a matter of time before Christianity became the official state religion, considering its gradually growing popularity in the Graeco-Roman world? Another is this issue: Was Constantine a 'real' Christian, or did he just adopt the religion for specific, pragmatic reasons? And there are other issues I'd love to have clarified. What was the reaction of the various strata of the population to Constantine's conversion and his decrees? How did Constantine get converted in the first place? How did all this affect the church hierarchy? When was the first pope consecrated, and how was power distributed between the emperors and the popes? etc etc
Not all of these questions are addressed directly in Fox's book, and I suppose I'd have to read or peruse dozens of texts before I got a proper handle on it all [always remembering too that the primary materials are so scant, and often one-sided and propagandist, that many questions will never be fully answered], but if I can trust Fox - and I feel inclined to do so -  I can at least answer the first two questions more or less to my satisfaction. Most of the following comes from Fox and from wikipedia articles on Constantine, his dad Constantius, Diocletian and others.

Constantine was born in 272. At the time, his father was a Roman officer, part of the bodyguard to the emperor Aurelian [270-275]. Interestingly, Aurelian, a highly successful emperor in spite of the brevity of his rule, raised the status of the sun god, Sol, as the main divinity of the empire, providing a first glimpse of European monotheism, though perhaps we shouldn't make too much of that.
Hard to know how much the young Constantine was aware of it all, but the empire was in a right mess during his early years - the last years of what has been dubbed by historians 'the crisis of the third century' - with seven emperors having dropped dead by his fourteenth birthday. The eighth emperor, Diocletian, a former army officer of 'low birth', eventually raised Constantius, the army officer of low birth, to the position of Caesar, or junior co-emperor. For some reason Diocletian decided, over time, to divide the empire into quarters. First, in 285, after only a year as emperor, he appointed Maximian as his senior co-emperor, or Augustus, and then in 293 he appointed Constantius and Galerius as junior emperors. My guess is that there were so many marauding peoples on the borders of the empire [Quadis, Sarmatians, Goths, Alamanni, Longiones, Franks, Burgundians and Vandals to name a few] that Diocletian realized he'd have to be in four places at once to keep his eyes on them.
Constantius was one of the western emperors. His son, the future Constantine, eventually joined him on campaign in Gaul and Britain, where Constantius died, in York, in 306. This was in the year after Diocletian retired to his vegetable garden [he was one of those rare top pollies who chose to turn his back on power]. The tetrarchy he created immediately came under strain. Constantine wasn't named Caesar after his father's death, and a complicated power struggle ensued. More importantly though, for the future of Christianity, Constantine, who was brought up in Diocletian's court, witnessed the early years of the Great Persecution, the worst persecution of Christians in the empire's history, a persecution begun by Diocletian and further pursued by Galerius and Maximin. It probably had a profound effect, and, while trying to consolidate power in the west, he took a more tolerant approach to Christianity, as his father had before him. He seems to have converted to Christianity around the year 312, probably under the influence of a close adviser, Ossius, bishop of Cordova. Ossius was to become Constantine's representative in the Christian disputes the emperor felt bound to deal with in the 320s, most notably the Donatist and Arian controversies. He also presided over the Council of Nicea in 325.
Anyway, to answer the two questions. Firstly, no, it wasn't inevitable that the Roman Empire would become Christian. It came as quite a shock in fact. Although we don't have clear data like censuses and the like, there's little evidence that Christianity was on the rise before Constantine's conversion, and of course the vast majority of the ruling class and the ranks of the military were pagan. It was also hardly inevitable that Constantine would survive to stabilize the empire, and to take it onto the road towards Christianisation. The fifty years before Constantine's rise to power were incredibly bloody and dangerous for emperors. Many were corrupt or incompetent, but many were brilliant, or at least potentially so. No doubt Constantine kept his wits about him, but he also would have had more than his fair share of luck, and Christianity itself was riding on this luck. But it should also be noted that Christianity was a vastly different religion from paganism. It was far more than just moving to a more monotheistic paradigm, as with the emperor Aurelian and his son-god. With Christianity came the concepts of sin, redemption, salvation, the Fall and the Second Coming, a way of looking at the world completely at odds with the pagan religion. For this reason, once the religion became established, disestablishing it - as the later emperor Julian tried to do - was something of a too-hard-basket proposition. So, given that, had Constantine not been persuaded that way, another later and successful emperor might have turned to Christianity, the religion still might have been successful without Constantine. Then again, maybe not. The best approach would've been to ignore the religion, rather than adopting it or persecuting it. And perhaps that's the best approach today - but it becomes difficult when a religion interferes with scientific theory, or campaigns against the furtherance of knowledge, as I believe the Catholic Church does.
As to the second issue, it's clear from his concern to iron out the problems with Christianity in the early fourth century, and his keenness to establish an orthodoxy, that Constantine was a sincere Christian. There doesn't seem to have been any obvious pragmatic motive for his conversion, which would've caused more logistical and process problems than not.