2015 will have three Friday the 13ths. I don't mean that Jason Vorhees is returning in a back-to-back cinematic triptych released faster and more furiously than anything in the Fast and the Furious franchise, but that there are three months in which the 13th falls on a Friday. To whit: February, March and November.

Surely that’s a fluke caused by that whole February-March collusion (the subject of another conspiracy, perhaps)—in the long run there should only be a one in seven chance of the 13th falling on a Friday. Right?

What if I told you that it can be proved mathematically that it’s not an even race, that Friday is more likely to be Black than any other day of the week? Suddenly it seems a little suspicious, doesn't it?

Yes, I know it sounds impossible at first. After all, 52 weeks doesn’t fit evenly into 365 days, so it tends to cycle through. Every day of the week should get a go at being the 13th.

But this is all complicated by leap years, that extra 29th February we get every fourth year. Except it's even more complicated than that, because turns-of-the-century are not leap years. Except it's even more complicated than that, because every fourth century there is a leap year, eg the year 2000.

Somehow this all works out to make our calendar match up with the Earth’s orbit around the Sun, although occasionally the time lords at Greenwich throw in an extra second to keep us on our toes. Watch out for it this year on 30th June, when 11:59 pm will have 61 seconds. (I would say to set your clock for that, but well, I don’t know how you can).

Anyway, the end result is that, according to Wikipedia, every 400 years of our calendar contains 146,097 days, which is 2,871 weeks exactly. So the distribution of days of the week is fixed in every 400-year block, therefore they can never exactly even out.

And it turns out that, over the 4,800 months in those 400 years, Friday the 13th occurs 688 times. That gives it slightly more than a one in seven chance; more like 1.003 in seven.

But, you protest, that's just the luck-of-the-draw, isn't it? For that to be a conspiracy it would have to have been rigged right from the establishment of the calendar!

That's exactly what I'm suggesting.

Our calendar system is known as the Gregorian calendar, established in 1582 by Pope Gregory XIII. Notice those Roman numerals: XIII = 13!

Having founded a whole calendar, Gregory XIII is rather well-known, as is his heraldic symbol, a dragon (actually a truncated dragon, which sounds to me like a drag). This rather devilish logo has over the years been fuel for many an anti-Catholic conspiracy theory, frequently comparing the pope to the Beast of Revelation, about whom it is written, "And they worshipped the dragon which gave power unto the beast, and they worshipped the beast, saying, Who is like unto the beast? Who is able to make war with him?"

Who indeed. And what chapter of Revelation do you think it is that bears this prophecy? I'll answer for you: it's Revelation 13!

(That’s also the chapter with the famous Number of the Beast, 666, but it’s hard to find a connection to 13 there. The best I can do is read 666 in base-13, in which it’s equivalent to 1098. And the only significance of that is that it was the year the First Crusade arrived in the Holy Land. Hmm…)

OK, so the existence of a conspiracy is proven beyond doubt, but how did it start? What is the meaning behind Friday the 13th?

According to scholars such as Dan Brown, in his authoritative work The Da Vinci Code, the suspicion around the date started on Friday 13 October 1307, when King Philip IV of France arrested Grand Master Jaques de Molay and sixty other Knights Templar. The Knights Templar, an order that was founded during—well bless my soul—the First Crusade.

It's well-known that all conspiracies begin with the Knights Templar.

Now whether there was an apocalyptic reason, beyond mere commemoration, for Gregory XIII—clearly a secret Knight Templar and probably a freemason too (like Sir Christopher Wren)—to set up the calendar like this, I cannot say. Notoriously secretive, these Illuminati. But I intend to keep looking for an answer, at least until they stop me.

All I can say is that it beats the alternative conspiracy theory about the Gregorian calendar—popular at the time of its inception—which is that it was a plot to cheat tenants out of a week and a half's rent.

I think we can dream a little bigger than that.


Pope Greg XIII, up to no good I'll wager.  Ospedale Santo Spirito in Sassia, Rome , published by Ditta Vasari Fotografo Editore. Said to be a fresco in the great hall of the Banco Santo Spirito in Rome, featuring Pope Gregary XIII. Wellcome Library, London, image number V0030917.

Pope Greg XIII, up to no good I'll wager. Ospedale Santo Spirito in Sassia, Rome, published by Ditta Vasari Fotografo Editore. Said to be a fresco in the great hall of the Banco Santo Spirito in Rome, featuring Pope Gregary XIII. Wellcome Library, London, image number V0030917.