Many Christians have long believed that Friday was unlucky because it was the day of the week when Jesus was crucified. The number 13 was believed to bring bad luck because there were 13 people at The Last Supper.
Thirteen was also a sinister number in Norse mythology. Loki, one of the most evil of the Norse gods, went uninvited to a party for 12 at Valhalla, a banquet hall of the gods. As a result, he caused the death of Balder, the god of light, joy, and reconciliation.
On Friday, October 13, 1307, King Philip IV of France ordered the arrests of Jaques de Molay, Grand Master of the Knights Templars and sixty of his senior knights in Paris. Thousands of others were arrested around the country. Most of the Templars were eventually executed and their sympathizers condemned Friday the 13th as an evil day.
In the 18th century, the HMS Friday was launched on Friday the 13th. It was never heard from again. Since then, ships are not usually launched on that date
It is considered especially unlucky to have 13 people at the table during a meal, such as in Agatha Christie's mystery novel, Thirteen at Dinner. During the 1880s, a men's group that felt superstition was an unhealthy influence on public life held Thirteen Club dinners.
President Franklin D. Roosevelt would not travel on the 13th day of any month and would never host 13 guests at a meal. Napoleon and President Herbert Hoover were also triskaidekaphobic, with an abnormal fear of the number 13.