Yes. Many did end up as fonts. The early churches, I'm talking ones founded around 600ce seem to have gravitated to them and/or their sites.

I think they were the largest form of ritual monument around at this period and *needed* to be assimulated by the early Xtian monks. The fact that St. Brigit (né Brigid) is the biggest thing in a lot of Ireland speaks volumes too. She's bigger than Christ, as big as Mary and even approaches Patrick levels of importance. There's more to this lady than meets the eye ...