There are plenty of superstitions out there, but none have woven themselves into the fabric of our culture quite like Friday the 13th. It’s inspired books, songs, and one of the most successful horror movie franchises of all time. But despite giving us anxiety, the origins of this notorious date on the calendar remain largely unknown to most. Where did it start? Does it really stretch back to the 14th century? And how does Loki figure into all of it?

There are a lot of urban legends and half-truths out there, so let’s dive a bit deeper into the history of this most terrifying of days with 13 facts about Friday the 13th.

1. The Bible is partly responsible for the phobia surrounding Friday the 13th.

Part of superstition surrounding Friday the 13th comes from the Christian Bible. During the Last Supper, there were 13 guests: Jesus and his 12 apostles—one of which, Judas, would eventually betray him. Since then, some have believed in a superstition regarding 13 guests at a dinner table. This slowly extended to be an overall feeling that the number itself was bad luck.

Of course, when Jesus was crucified, it took place on a Friday, leading some to view the day with an anxious eye. Taken separately, both the number 13 and Friday have since made their way into modern superstitions.

2. Loki also played a part in inspiring fear of Friday the 13th.

The Last Supper is one view on the origins of our fear of 13. Another comes from Norse mythology—more specifically in the form of the trickster god Loki. In those stories, Loki tricked the blind god Höðr into killing his brother Baldr with a dart of mistletoe. Baldr’s mother, Frigg, had previously ordered everything in existence to never harm her son, except the mistletoe, which she viewed as incapable of harm.

How does 13 figure into this? Some accounts say Baldr’s death took place at a dinner held for 12 gods before it was interrupted by Loki—the 13th (and most unwanted) guest.

3. Some point to the Knights Templar as the source of why people fear Friday the 13th (but it’s probably not true).

Contrary to what The Da Vinci Code told you, the reason people fear Friday the 13th isn’t because of the Knights Templar. On the very unlucky Friday, October 13, 1307, Philip IV of France had members of the Templar arrested—he was growing uneasy with their power and covetous of their riches. There were trials, torture, and many of the Knights were burned at the stake, eventually leading to the superstition of Friday the 13th as a cursed and evil day.

That’s not quite true, though. This is a take that’s been drummed up in recent years, most visibly in Dan Brown’s best-selling novel, but in reality, the unlucky combination of Friday and 13 didn’t appear until around the turn of the 20th century.

4. A 1907 novel played a big part in creating the superstition.

We know a good deal about the history of our fear of 13 and of Fridays, but combined? Well, that’s less clear. One popular thought, though, points to a 1907 book by a stockbroker named Thomas Lawson. Titled Friday, the Thirteenth, it tells the tale of a stockbroker who picks that particular day to manipulate the stock market and bring all of Wall Street down.

The book sold fairly well at the time, moving 28,000 copies in its first week. And it must have struck a chord with early 20th century society, as it’s said to have caused a real-life superstition among stockbrokers regarding trading and buying stocks on the 13th. While not the first to combine the dates, Lawson’s book is credited with popularizing the notion that Friday the 13th is bad news.

The fear among brokers was so real that a 1923 New York Times noted they “would no more buy or sell a share of stock today than they would walk under a ladder or kick a black cat out of their path.”

5. Stockbrokers have reason to be nervous on Friday the 13th.

Lawson’s book was pure fiction, but the history of the stock market on Friday the 13th can be either profitable or absolutely terrifying, depending on the month. On most Friday the 13ths, stocks have actually risen—according to Time, they go up about 57 percent of the time, compared to the 52 percent on any other given date. However, if it’s a Friday the 13th in October … be warned.

There’s an average S&P drop of about 0.5 percent on those unlucky Fridays in October. And on Friday, October 13, 1989, the S&P actually saw a drop of 6.1 percent—to this day, it’s still referred to as a “mini crash.”

6. Good things happen on Friday the 13th, too.

On Friday, July 13, 1923, the United States got a brand new landmark: The famed Hollywood sign was officially christened on that day as a promotional tool for a new housing development. But before the sign took on its familiar image, it initially read “Hollywoodland”—the full name of the development that was being built on the hills above Los Angeles. The sign took on its current “Hollywood” look in 1949 when, after two decades of disrepair, the Hollywood Chamber of Commerce decided to remove the last four letters and just maintain the first nine.

7. Appropriately, heavy metal music was born on Friday the 13th.

This one isn’t exactly scientific, but don’t tell that to a metalhead. According to heavy metal lore, the genre was born Friday, February 13, 1970, with the UK release of Black Sabbath’s self-titled debut album. Bands like Steppenwolf had laid the foundation in the years before (Steppenwolf is also credited with coining the term heavy metal in their lyrics for 1968’s “Born to Be Wild”), but those first dissonant “Devil’s Tritone” chords of “Black Sabbath” were the true birth of the dark, brooding, rocking subculture. Horns up.

8. There are scientific terms for the phobia.

You likely already know the term triskaidekaphobia, which only applies to the fear of the number 13. But for specific fears of Friday the 13th, you can choose between paraskevidekatriaphobia (Paraskevi means “Friday” in Greek) or friggatriskaidekaphobia, based on the word Frigg, the Norse goddess that Friday was named after in English. (Remember, it was her son who Loki had killed … )

9. One Indiana town puts bells on every black cat to ward off bad luck.

The folks of French Lick, Indiana—a.k.a. Larry Bird’s hometown—are apparently a superstitious lot. In the 1930s and into the ’40s, the town board decreed all black cats in the town were to wear a bell around their neck every Friday the 13th. Apparently, the confluence of two popular phobias was a bit too much for the small Indiana town to handle.

10. Five presidents were part of a club to improve the number’s reputation.

Some people aren’t just unaffected by the stigma of 13, they’re downright defiant of it. In order to prove that there was no curse on the number, Captain William Fowler—who had fought in 13 Civil War battles—started a club in 1882 that spat in the face of superstition.

Members would meet on the 13th of the month, at 13 past the hour, and sit 13 at a dining table. For some, this behavior was just begging for a hex, but these men didn’t care. They sought to disprove the myth and others along with it—open umbrellas lined the dining hall and members would willingly break glass, waiting for a so-called curse to befall them.

This wasn’t just a club for eccentrics, either. Five presidents would become honorary members of The Thirteen Club: Chester Arthur, Grover Cleveland, Benjamin Harrison, William McKinley, and Theodore Roosevelt. In fact, Cleveland would take part while he was in office. In all, it's said that no man was struck down by any particularly curious fate (except perhaps McKinley, who was assassinated), despite having so blatantly tempted it.

11. In Italy, people fear Friday the 17th.

Traditionally, Italy’s fear coincides with the number 17, which can be arranged as the sum of the Roman numerals VIXI, which can then, in turn, be translated as the Latin phrase I have lived. The overall superstition around Friday remains the same—it all has to do with Jesus’s crucifixion.

This is no niche phobia, though. As ThoughtCo. points out, there are people who refuse to leave the house or go to work on Friday the 17th out of fear of the ominous date. And the Italian airline Alitalia doesn’t even put a row 17 (or a 13) on its planes.

12. There can’t be more than three Friday the 13ths in a given year.

There’s some good news if you’re one of those people who are genuinely afraid of Friday the 13th: There can’t be more than three in any given year, and it’s possible to go as many as 14 months without one. There’s an easy way to figure out if a month will have a Friday the 13th, too—if the month starts on a Sunday, you’re guaranteed one.

13. An asteroid will come relatively close to us on a Friday the 13th in 2029.

Let’s just get this out of the way: We’ll be fine. An asteroid will not collide with the Earth on Friday, April 13, 2029. We will, however, get a pretty spectacular look at asteroid 99942 Apophis (also known as 2004 MN4), which is about 320 meters wide and would be devastating if it did hit. When the asteroid was first discovered in 2004, astronomers gave it a haunting 1-in-60 chance of colliding with Earth, but extra data has proved that it will miss us entirely.

“We weren’t too worried,” Paul Chodas, of NASA’s Near Earth Object Program, said, “but the odds were disturbing.”

That’s not to say the asteroid still won’t be a sight to behold: Apophis will cruise past Earth 18,600 miles above ground. “For comparison,” NASA wrote on its site, “geosynchronous satellites orbit at 22,300 miles.” The asteroid will be mostly visible in parts of Asia, Africa, and Europe, and another event of this nature may not be seen for another 1000 or so years.

A version of this story ran in 2018; it has been updated for 2023.

This article was originally published on www.mentalfloss.com as 13 Fascinating Facts About Friday the 13th.