Grimms Fairy Tales (I know this has been done to some degree but not extensively)
I'm a big fan of fantasy so the additon of more fantasy elements/creatures is fun to me. I love the dragon and fan made giant that is being developed. Maybe other fantastic creatures? Werewolves, demons, vampires, ghosts...
What about Arabian Nights and the tales told by Sherherazade? It might fit better with Ark of the covenant, though, being in the correct geographical location as opposed to France.
Also, the Legend of the Templars could work very well, if tied in with the legend/backstory from The Da Vinci Code - the legends that the Holy Grail once made it to France.
Or, you could do something involving the Crusades, such a tile (or something) that triggers an event that causes all knights to leave their incompleted cities to fight in the Crusades.