There are masonry techniques that are considered lost arts is probably what he's referring to, including types of load bearing cobblestone construction. An exa

There are masonry techniques that are considered lost arts is probably what he's referring to, including types of load bearing cobblestone construction. An example that comes to mind is a brick townhouse nearby that was struck by a car and part of a structural brick rounded wall collapsed. It remained that way for many years because the owner simply couldn't find a mason that knew how to rebuild it.