It is no secret that most churches were built on the site of pagan shrines. The general given reason for this is that the local population would be more ready to frequent the new building if it was sited where their old shrine was, but it is more likely that these sites were situated on places of power, something the church builders (masons) knew.
Yes, quite possibly. We had fun looking at many churches in South France (and we do this here in Germany as well).
Some pagan symbolism was supposedly incorporated into these old churches and cathedrals. We are getting into Da-Vinci code territory here. 
"Symbols" are often what people make of them. One thinks the pentagram is a magical sign - then it is for him. Others may think it symbolizes 5 wounds of Christ or Mary Magdalene or Venus...
Leonardo da Vinci painted quite a few "religious" paintings. But I think he wasn't always agreeing with Catholic dogma, so e.g. he was examining dead bodies even if the Church told him not to...
Anyway I am not an expert but I do find it interesting that there just may have been an ancient race who lived in harmony with the earth rather than exploit it, and who’s existence has been erased from history. That some of their monuments still exist to this day is remarkable. 
As soon as "power hunger" takes over, humans often exploit the earth or their fellow humans...

But I agree, ancient cultures are often fascinating and I like to look at old buildings, stones, art etc.
Nearly all old Christian churches and cathedrals have Pagan Gargoyles (the one's water comes out of), Pagan Grotesques ...
Indeed, though they're supposed to be "demons" to keep evil spirits away (or something like this). They might have used "Pagan" images for those.
That's true the Christian Church did not wipe out pagen beliefs it often just assimulated them just think of Christmas...
Yeah, just like churches were built on other "holy" places, the old festivities were assimulated too...
Let's not forget though, many of the archeologists we have today grew up in "Christian" churches, schools and Unis. Things did become better with the "Age of Enlightenment".
