Sorry, no facts about the possible Christianisation, but did you notice the fence? The photos you linked to have what looks like a metal post and rail but when I was there a few months ago (strangely enough, to look at the fence as an example of what to put around a monument), there was this cattle smashed chain wire thing on wooden posts with a nice little trench scooped all the way round the outside by busy hooves. All topped off by a fresh dollop of cow dung right inside beside the pillar.
Lovely.