The Knights Templar achieved great influence in Europe between 1096 and 1307. Their downfall came on Friday 13th October 1307. This date saw the catastrophic destruction of the Knights Templar at the hands of King Philip of France and his puppet Pope Clement V. Some say this event, in which the Templars were burnt at the stake, gave birth to the superstition associated with Friday 13th.
A superstition that if 13 people sit down to dinner together, all will die within the year. The origin of this legend dates back to the Norse god of mischief - Loki. The saga tells of Loki gate-crashing a party bringing the number of guests to 13. To cut a long saga short, Balder the good was killed. For this reason Norwegians believe that 13 at a dinner party is bad luck.
Because there are precisely 13 witches in a coven.
The Bible, Luke's Gospel Chapter 22, tells us that there were 13 present at the Last Supper. There is evidence that this Last Supper was held on a Friday, and of course this is when Judas Iscariot betrayed Jesus Christ to the Romans.
A baker's dozen consists of 13 for a reason! So the story goes a witch near Albany, NY demanded 13 items every time she came in to a particular bakery, and one day the old baker could not afford her extra biscuit. She sneered some strange words at the man, and he suffered terrible luck from then on, until he brought her another 13 rolls. After that life was once again easy for the baker and word spread around town. The custom is still sometimes practiced today.