Indulge yourselves for a moment..
The cross is carved with alchemical symbols that occultists find to contain encrypted information on a future global catastrophe.
 See also
so on to Fulcanelli
This doesn't explain much at all about the work itself that ties him to the cross, but the book entitled "Mystery of the Cathedrals" explains the links to Gothic Cathedrals being clues to Ancient Alchemy secrets.. But what is even more interesting than that is his connection between Alchemy to the spiritual path to dissolving the ego...and how we are moving to a new age which will require this transformation..
A lot to swallow I know, but hear this guy out on how he made the connections, then check it out and share your thoughts.. if it's all B.S. it's better than the The Da Vinci Code!