Even a scraping off the concrete would tell us who made them. The romans used a lime based material and the monks used a lesser proportion so it would be easy to establish the origin. There are no signs of entry anywhere so we gather it came via an apse behind the altar. Jimmy and I have 3d pictures of the church showing every stone, which has been dated and where it was hewn. The only problem doing such research on churches is becomes addictive and we tend to go too far at times.