According to some, the Cathars held secret religious beliefs Christians and similarly-aligned religious despots believed heretical. The Cathars, so it is said, thought themselves to be the good guys -- as those with deeply-held religious beliefs often do -- opposed to the evil god of the material world, who the Christians worshiped. Some say the Cathars Perfecti were vegetarian celibates whose initiates were allowed to eat fish. Some of their beliefs may have been Islamic in nature, suggesting to some scholars that they were converts to Islam.
If all of this sounds strangely familiar, it's because a lot of this appears to have been taken -- possibly confused with, or possibly presented as counter-intelligence -- from the history of the [then Roman-]Catholic Church. In fact, Rome is said to have been the most stringent opponents of Catharism. There was also a small congregation of vegetarian women in England known as The Shakers who remained celibate (and their cult is said to have died because of this).
Some time in the mid 13th-Century, the last remaining stronghold of the Cathars was felled. Some of them were said to have absconded with a secret treasure the Knights Templar (and others) believed to have been The Holy Grail -- or a mummified cockatrice known as "Baphomet," which the Knights Templar were later said to have worshiped. Discrepancies as to where the word "Baphomet" comes from remain, but the mummified remains could have been dinosaur bones, and the remains of animals not native to Europe, that scholars of the day pieced together incorrectly, basing their assumptions on their provincial knowledge. The Cathars who survived the night are said to have surrendered the following day and they were immediately burned at the stake.
The Knights Templar may or may not have been the very force which drove the Cathars from their roost, and continued to pursue them to retrieve their secrets and treasure, but the two cults were almost certain to have had some contact during their eras of activity. In fact, following the Cathars' fall, many may have become Knights Templar, as some scholars say the Cathars had been entirely eliminated by the end of the 13th-Century, while the Knights Templar are said to have persisted until the early 1300s. There seems to be little information regarding the Knights Templar prior to the Cathars, and either may have been converts to Islam.
In the early 14th-Century, the King declared the Knights Templar heretical and killed them all, as well, after torturing them into "Confessing" to alleged crimes they may or may not have committed. At any rate, the date on which the last of the Knights Templar were either first attacked, or finally murdered, is said to have been Friday the 13th.
The Antipope Nicholas V ascended on Thursday the 12th, 1328.
Now, all of this is hard to confirm -- especially online -- and I may well have much of it confused, but it is interesting enough to post (as I've been meaning to do many times before). Remember that although I try to research what I can to ensure you are getting plausible information, I do not have all the answers -- nor even the right questions! In fact, this post from the venerable Mental Floss (UK, apparently) sheds more light on this traditionally "unlucky" day which mentions none of this, and may well be correct. However, the connection to the ascendancy of the "Antipope" is likely the smoking gun behind this superstition.
© The Weirding, 2016