What is "Gallia Christ"?

I keep finding "Gallia Christ" referenced in historical documents, but I can't find out what or where it is. It seems to be a historical book of many volumes. Google just brings me more documents that reference it, but no clues about where to actually read or research using it. Any ideas?

I'm feeling very idiotic today.

Thanks! Now I'm rolling again! That makes sense in the context; I'm trying to find out where two of Henri II of Navarre's sisters (both nuns) were in 1526. Gallia Christiana is apparently a census of French religious houses.