Today is Friday the 13th. For some, it's considered a day of bad luck. Many historians believe it was unlucky because it was the day when Jesus was crucified. The number 13 was believed to bring bad luck because there were 13 people at the Last Supper.  

According to the stress management and phobia institute, between $800 and $900 million are lost in business each Friday the 13th, because of people who won't work or travel.

Fear of  Friday the 13th dates back to Nordic mythology. Many of their thirteenth gods met with violent deaths, such as Loki, the Trickster. 

Ancient Romans regarded the number 13 as a symbol of death, destruction and misfortune.

Lizzy Borden uttered a total of 13 words at her trial.

There were 13 original colonies.

A witches coven consists of 13 members.

Tarot card number 13 is the death card, depicting the grim reaper (although it is read as transition or change and not literal death).

Hotels rarely have a room number 13. Usually it is called 12a or 14. Same with floors of buildings and the elevators without a #13 button. Highways sometimes will skip exit 13 altogether also.

There are 13 steps leading to the gallows.

13 knots in a hangman's noose.

13 feet which the guillotine blade falls.

The driver of  Princess Diana hit pillar #13 at Place de l'alma when she was killed in Paris, France.

Certain ocean liners will be held in dock until after midnight to appease passenger's fears on Friday the 13th.

British study concluded that even though there were less cars on the road on Friday the 13th (as compared with other fridays) more accidents were reported.

Trisadekaphobia is the technical name for fear of  Friday the 13th.

Apollo 13, 1970, the 13th mission launched from pad #39 (13 x 3), mission was aborted, after an explosion occurred in the fuel cell of their service module. The rocket had left launcing pad at 13:13 cst and the date was April 13th.

Epluribus unum has 13 letters.

The U.S. seal has 13 stars, bars, feathers in the eagle's tail, 13 bars in one claw, 13 olive branches in the other.

A "quatrorzieme" is a professional 14th guest hired by the French who had only 13 guests in attendance for dinner, who felt that was unlucky.

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.