In a documentary I am watching, it is said, that Constantine had a vision of a cross and letter P, and heard some voice, they say that the Christian God Himself, that told him, that with this symbol he will win the war against usurpator Maxentius. So he painted this symbol on the shields of his men, fought against the army of Maxentius, and won. This made him realize that this Christian God is stronger than the Roman Gods, and so he converted to Christianity.
How accurate is this statement? Isnt this just too much speculation, and a little biased? What I know about Pagan religions, it is that they are very syncretic, meaning there is no rule like "You have to worship only the true Roman Gods, and no others!" Actually, the Romans had no problem worshipping a lot of Gods from different Pagan religions. Like one day a Roman citizen made a sacrifice in the temple of Isis, and then the other day this Roman citizen made a sacrifice in the temple of Jupiter. This is what my professor of history tought us, at least. The Roman Gods dont care if you worship another Gods as long as you make sacrifices for Them too, right?
So didnt Constantine just do the same thing when he got the vision? Wasnt he more like "Oh, this Christian God is giving me an advice how to win this war, great, I will worship him beside worshipping other Gods." And so he just added a new God to his pantheon, because why not? What makes historians believe that Constantine fully embraced Christianity and rejected all other Gods? I read documents from Eusebius, but that seem like a lot of Christian propaganda to me, I cant take him seriously. Are there any other sources, more objective, that proves that Constantine was the first Christian Emperor?
Besides, wasnt Constantine baptized on his deathbed? That is hardly something a devouted Christian would do...
Thanks for all your answers!
There are a lot of questions here, so let's take them in turn.
The sign which Constantine saw was the Chi-Rho, so not just Ρ, but also Χ together. He heard the voice from Heaven saying, "Εν Τούτῳ Νίκα" ('In this [sign] conquer'), sometimes translated into Latin as, "In hoc signo vinces" ('In this sign you will conquer'). One of the issues surrounding this story is that it's given to us by Eusebius only in his later Vita Constantini (Life of Constantine) (I.28.9), written in 339, two years after Constantine's death, and is absent in his account of the Milvian Bridge in the Historia Ecclesiastica (Ecclesiastical History). Nevertheless, Eusebius does say in the HE that Constantine won by virtue of his faith in the Christian God (HE IX.9.3). The latter story about the vision could very well have come simply from his having been in contact with the Emperor personally (cf. T.D. Barnes, "Panegyric, History, and Hagiography in Eusebius' Life of Constantine" in R. Williams ed., The Making of Orthodoxy: Essays in Honor of Henry Chadwick (Cambridge, 1989)).
Besides, wasnt Constantine baptized on his deathbed? That is hardly something a devouted Christian would do...
This is actually something that's incredibly common in the 4th century and something against which you find 4th century Bishops in both East and West preaching against. Augustine himself encourages people not to delay their baptisms (as he had done). For this, look at G. Nyssa's On the Baptism of Christ.
The Roman Gods dont care if you worship another Gods as long as you make sacrifices for Them too, right?
The syncretism of the Roman Empire is interesting. It's not simply religious, but is socio-political. When the Romans would defeat a group of people and then import their gods, the implicit message to the defeated peoples is that they were not pious enough towards their own gods and this was the reason for their defeat. The assimilation likewise was not a simple co-opting, but rather a subjugation of the foreign gods to the Roman imperial powers (cf. Beard, North, and Price, Religions of Rome: Vol. 1).