According to http://www.kidsturncentral.com/holidays/friday13.htm:"The
modern reason for this is said to come from Friday October the 13th, 1307.
On this date, the Pope of the church in Rome in conjunction with the King of
France, carried out a secret death warrant Against "the Knights Templar".
The Templars were terminated as heretics, never again to hold the power that
they had held for so long. There Grand Master, Jacques DeMolay, was arrested
and before he was killed, was tortured and crucified. "
picture from www.mediabistro.com