Originally Posted by Supervox

IIRC the REAL reason that Fri 13th is considered unlucky - at least in the western world - is because that was the date that the King of France launched his surprise attack & rounded up the Knights Templar.

This had nothing whatsoever to do with religion (although that was the official reason) - more to do with the fact that the Templars were probably the richest organisation in Europe at the time & he fancied getting his hands on the loot - oh, & also because he owed them a truck load of money for financing his various wars, etc.

Originally Posted by Friday 13th link

There are drawbacks to the "day so infamous" thesis, not the least of which is that it attributes enormous cultural significance to a relatively obscure historical event. Even more problematic, for this or any other theory positing premodern origins for Friday the 13th superstitions, is the fact that no one has been able to document the existence of such beliefs prior to the 19th century. If people who lived before the late 1800s perceived Friday the 13th as a day of special misfortune, no evidence has been found to prove it. As a result, some scholars are now convinced the stigma is a thoroughly modern phenomenon exacerbated by 20th-century media hype.