I read in wikipedia some time ago that the traditional Pagan Lithuanian religion had remained prominent in Lithuania all the way through the 16th century, and there were still sizeable, though comparatively small, populations in Lithuania following Paganism well into the 18th century. I was wondering, in other countries that converted earlier and more willingly, were such practices still common for such a long time after the conversion? In the late middle ages, was it still possible to find entire villages following traditional Norse religion in, say, Sweden?
What you would find is that Christianity would become a sort of overlay over the traditional beliefs of the people. When I was researching the Vendee in the 18th Century I found that there had been a kind of missionary movement in the region throughout the earlier part of the century to re-establish conventional catholicism as the paganism had become to obvious to be allowed to continue. There were examples of saints who had animal forms, with antlers or horns, sacred groves in the forest, sacred pools, sacred springs, places that were sacred to a saint that the Church had never recognised. Holy days that involved gifts of flowers to a particular tree, things like that. This certainly supports the argument that the Church simply adapted existing rituals and religious expressions and made them part of their own set of traditions. Rather like Christmas taking over from Yule and Saturnalia.