The Constantine breakthrough was the beginning of changes in the whole Roman Empire state system. In Roman Law that process meant the introduction of Christian elements into legislation. The process of Roman Law Christianization was started by the Emperor Constantine the Great and was proceeded by his successors. The scope of those changes is difficult to determine. It is even more difficult to determine those changes mechanism of introduction. It is sure that Church was not the initiator of them. Even priests not always had been satisfied with those changes. Simplifying, those changes could be reduced to three areas: law and rules regarding the Christian cult; respecting the Christian spirit laws, and, finally, to, so called, privileges which were bestowed to the Catholic Church. It seems to be that this process did not open the way to introduction of confessional state but strengthened its tolerant – in religious case – character. This article is a systematization attempt of these issues, especially in the face of the numerous appearing allegations.