The Baptistery of St John in Poitiers is claimed to be the oldest existing Christian building in France. Built in about 360 but much altered, it is worth half an hour (at least) of anybody's time.
For a plan of the building, there is a good link here, and for more information check out Wikipedia
We Love Photographers! - We think the Touraine Loire Valley is fabulously photogenic and we take about a thousand photos a month to prove it. Consequently, we love it when serious ...