Friday the 13th is not a superstitious day for me but it was for the Knights Templar and many Christians, which is believed where the superstition started because...

Knights Templar History - Knights Templars are charged with Heresy
King Philip IV of France (1268-1314) who was already heavily in debt to the Knights Templar requested a further loan. The Knights Templar refused his request. King Philip IV subsequently ordered the arrest of all Knight Templars in France. The order to arrest the Templars was sent out several weeks before the date possibly giving the Templars time to hide their wealth. On 11 October, two days before the arrest of many Templar Knights, it is recorded in French Masonic history that Templar ships left La Rochelle, heading to Scotland. On Friday the 13th, in October 1307, Jacques de Molay, the Grand Master of the Knights Templar, and 60 of his senior knights were arrested, tortured, and killed in Paris. They were charged with heresy and accused of homosexual acts. Admissions of guilt were extracted due to the use of torture. Pope Clement V initiated enquiries into the order and thousands of Knights Templar were arrested across Europe. Anyone found sheltering a Templar was under threat of excommunication. Much of the Templar property outside of France was transferred by the Pope to the Knights Hospitallers, and many surviving Templars were also accepted into the Hospitallers. The Medieval order of the Knights Templar become extinct in 1312 when the order is dissolved by the Council of Vienne.

Excerpt from: http://www.middle-ages.org.uk/knight...ar-history.htm