Constantine created Catholicism to solidify imperial control against a growing tide of Christian dissidents at a time when Roman authority was becoming harder to maintain due a number of factors. National religions have a habit of trading deities and mixing cult elements when they conquer other nations. The Nazi regime co-opted Christian imagery for instance and Hitler often referred to himself as Christian even using anti-semitic elements in Luther to justify his racial theories.
It makes things easier when the imperial group can create a pseudo-historical/mythological basis for their right to rule by co-opting common symbols. It also allows them to infuse old symbols with new meanings to produce a desired social change. In pop-culture terminology this is known as "frame jacking" and in the social sciences it is referred to as "social engineering".
There is a strong gnostic current in the Catholic church...very strong..and Mary fit pagan conceptions of Isis (the Greco-Egyptian equivilant of a number of pagan "mother" deities found across the Middle East and Asia minor who were mixed together as Roman imperialism spread across Europe, Asia and Africa).
The Catholic worship of Mary is often referred to by historians as the "Cult of Mary" and throughout the Middle Ages and Renaissance was the vehicle for these gnostic ideas to find acceptable practice in the Judeo-Christian world.
Since, for the most part, the Catholic clergy were the only group that could read, it was easy to mix elements of gnostic/pagan religion in when they were relating their interpretation of the Bible to the people.
The rejection of this mixture is what lead to the martyrdom of so many saints as detailed in the Trail of Blood article posted by Greg in another section of the forum.
