Triskaidekaphobia (from Greek tris meaning "3", kai meaning "and", deka meaning "10" and phobia meaning "fear" or "morbid fear") is fear of the number ; it is a superstition and related to a specific fear of Friday the 13th, called paraskevidekatriaphobia or friggatriskaidekaphobia.
There is a myth that the earliest reference to thirteen being unlucky or evil is from the Babylonian Code of Hammurabi (circa 1780 BCE), where the thirteenth law is omitted. In fact, the original Code of Hammurabi has no numeration. The translation by L.W. King (1910), edited by Richard Hooker, omitted one article:
If the seller have gone to (his) fate (i. e., have died), the purchaser shall recover damages in said case fivefold from the estate of the seller.
Other translations of the Code of Hammurabi, for example the translation by Robert Francis Harper, include the 13th article.
Some Christian traditions have it that at the Last Supper, Judas, the disciple who betrayed Jesus, was the 13th to sit at the table. However, the Bible itself says nothing about the order at which the Apostles sat. Also, the number 13 is not uniformly bad in the Judeo-Christian tradition. For example, the attributes of God (also called the Thirteen Attributes of Mercy) are enumerated in the Torah (Exodus 34:6–7). Some modern Christian churches also use 13 attributes of God in sermons.
Triskaidekaphobia may have also affected the Vikings—it is believed that Loki in the Norse pantheon was the 13th god—more specifically, Loki was believed to have engineered the murder of Balder, and was the 13th guest to arrive at the funeral. This is perhaps related to the superstition that if 13 people gather, one of them will die in the following year. Some French aristocrats would hire themselves out as the fourteenth diner at an event, because it was believed that when thirteen diners sat together, one of them would later die. Another Norse tradition involves the myth of Norna-Gest: when the uninvited norns showed up at his birthday celebration—thus increasing the number of guests from ten to thirteen—the norns cursed the infant by magically binding his lifespan to that of a mystic candle they presented to him.
Ancient Persians believed the twelve constellations in the Zodiac controlled the months of the year, and each ruled the earth for a thousand years at the end of which the sky and earth collapsed in chaos. Therefore, the number is identified with chaos and the reason Persians leave their houses to avoid bad luck on the thirteenth day of the Persian Calendar, a tradition called Sizdah Bedar.
On Friday 13 October 1307, the Knights Templar were ordered to be arrested by Philip IV of France. A theory has been suggested, in the book Born in Blood: The Lost Secrets of Freemasonry by John J. Robinson, that the Templars went underground among masons in England and later developed into Freemasons. Because a few of the founding fathers of the United States of America were Freemasons, it is possible that the memory of that day is preserved in the Friday the 13th.
In 1881, an influential group of New Yorkers led by U.S. Civil War veteran Captain William Fowler came together to put an end to this and other superstitions. They formed a dinner cabaret club, which they called the Thirteen Club. At the first meeting, on Friday 13 January 1881 at 8:13 p.m., 13 people sat down to dine in room 13 of the venue. The guests walked under a ladder to enter the room and were seated among piles of spilled salt. All of the guests survived. Thirteen Clubs sprang up all over North America for the next 40 years. Their activities were regularly reported in leading newspapers, and their numbers included five future U.S. presidents, from Chester A. Arthur to Theodore Roosevelt. Thirteen Clubs had various imitators, but they all gradually faded from interest as people became less superstitious.