One of the sources of the bad-luck connotation on Friday the 13th dates back to 1307. On Friday, October 13, the Knights Templars were captured by the marshals of King Filip of France. The King of France sent sealed letters to his marshals, describing they had to arrest the Templars for heresy.
The letters were only to be opened on October 13th. Nevertheless, some were opened before that day, and the message leaked out. So the Templars could escape with their famous treasure from Paris to La Rochelle. La Rochelle was the harbor of the fleet of the Templars. The legend states that 18 ships sailed from La Rochelle with the treasure, ... and so far not found!