Was thinking over some possible story ideas and I wanted to try to incorporate the introduction of some pre-Islamic Arabian paganism into Europe.
I had the idea that maybe Constantine had a manservant or some type of subordinate who was a Meccan by way of Petra perhaps who was a worshipper of Al-illah and who influenced Constantine to become interested in the religion of 'the Hanif' in some capacity.
Now, I don't think Constantine saw a vision or anything like that, but what if a prebattle stress nightmare seems to reveal a symbol identified with Al-illah and Constantine then is victorious?
My thinking was that this cult (at the time) would be appealing for a few reasons, namely its relatively close in many ways to the other Abrahamic faiths at the time while simultaneously being relatively close to various pagan faiths popular at that time from Europe to Persia, it's just obscure enough to be organized and controlled by Constantine and just exotic enough to become fashionable.
Him calling a council that includes people of many faiths to organize his vision of Allah's true faith should give him more control over its narrative and practical applications. Here, Christianity ceases to be persecuted, in honor of his mother, but becomes illegal. This new faith cannot immediately become the state religion, since it's foreign and new, but it can begin to infiltrate the masses during his lifetime.
The way I envisioned the faith is essentially Islam without the dietary restrictions and, of course, without Muhammad, with perhaps Constantine himself loosely filling that role. I imagine that Jesus' role might be slightly more respected in this canon, with him remaining a mortal prophet but perhaps allowing for the possibility of his being the son of Allah and him actually dying on the cross. I also think some aspects of lesser gods being changed into Angels, djinn, Saints, etc. might be possible to allow for feast days and appease the pagans.
I also thought about having Crispus be exiled to Arabia instead of killed here. He stays for a while with the Arabs, learning the old faith, fighting with them, and fathering children with concubines before returning to claim the Empire following his father's death. I thought perhaps under Crispus' rule the new religion could become mandatory. Christians, Pagans, and Jews who refuse to convert flee the empire or live in secret. Crispus is able to unite the Arab tribes under the Roman banner to help take on Persia.
Crispus' son marries a few Arab Chieftain's daughters and sires heirs and bastards alike with them and his concubines before 'marrying Roman' and ascending the throne. The royal line of Constantine begins to Arabize as does Europe (and vice versa) as criminals, slaves, and prisoners from Europe are sold as slaves to the Arabs as well as the reverse, the old trade roads are opened and become vibrant again, and Arab and European soldiers serve in one another's territories fostering mutual immigration.
Not sure how likely any of this is so I won't get carried away. Just wondering if anyone thinks it's at all possible or has any ideas.