Get some sage at the ready, because today marks the ominous Friday 13th. The day has long been marked as a particularly unlucky one for hundreds of years, but the precise origin of the superstition remains unclear.
The 13 part of it is not confined to the Friday 13 superstition. Skyscrapers will often eschew a 13th floor, opting to jump from 12 to 14, while airlines will also often skip row 13 on passenger jets.
But what about the Friday part? One possible explanation is the Last Supper, where Jesus sat down with 12 disciples meaning that there were 13 diners, before he was crucified on Good Friday.
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Nonetheless, the superstition around the number 13 itself is not universal. For example in Italy it is not Friday 13 but Friday 17 which is considered to be the unlucky day, with one explanation being that the Roman numerals XVII can be rearranged to "VIXI", Latin for "I have lived".
In China the number four receives the same treatment as 13, with buildings skipping the fourth floor. This is because the pronunciation of the number four is very similar to the word for "death" in Mandarin.
Meanwhile the number 39 gets a bad rap in Afghanistan. In Dari, the dialect of Persian spoken in North and West Afghanistan, the word for 39 can also be used to refer to a pimp, and is viewed with distaste as a result.
All these numerical superstitions have very clear reasons for being viewed with fear or distaste. However, with the number 13 in Western culture the origin is less obvious.
We've already talked about the Christian origin. This refers to the 13 diners at the Last Supper, with 13 coming to be associated with the somewhat unfairly put upon Judas Iscariot, without whom Christ wouldn't have died to redeem humanity's sins.
There is also another mythological root in the Norse pantheon which refers to a dinner of twelve Gods at which a 13th guest, interpreted by some to be the mischievous Loki, turned up uninvited. In a striking similarity to the notoriously plagiaristic Christianity, one of the gods at the table is told to have died after the dinner.
Friday 13 is also seen by some as being associated with the destruction of the Knights Templar. This happened when King Phillip IV of France arrested hundreds of Knights Templar on Friday 13 in 1307.
But the bad associations with the number 13 don't stop in mythology and medieval history. In more recent history it was the Apollo 13 mission which resulted in one of the most widely known space-related quotes: "Houston, we've had a problem here".
Such is the reputation of Friday 13 in the USA that some people have even speculated that it has a noticeable economic impact as employees call in sick or people cancel travel tickets. However, others have dismissed the claims that it has quite such a large impact as exaggerated.
The number 13 crops up in lots of places. Perhaps rather than one specific origin this is an example of a cultural trope which has snowballed from a number of different influences and become a widely held modern superstition as a result.
