It's a pity when I can't find much information about a really wonderful card... This one shows the fortified churches in Aisne region in France. The only information that I could find is that there are indeed many fortified churches, but that's all.
It seems to me that these churches were built in the romanesque style (correct me, if I'm wrong - I'm not so good at architecture). In Poland we don't have many buildings in romanesque style, because the country wasn't very good developed in the early middleages, but the ones that we have (mostly churches) were built of stone. The ones in France were built of brick, which looks really interesting. Or maybe it's not romanesque style and I'm just trying to pretend that I have some idea about it? :))