A new book tracks the history of the mediaeval Kingsman agents: the Knights Templar.

For generations, people have considered Friday 13th unlucky: the sort of day to stay in bed, far beyond the reach of innocently placed ladders, falling pianos, broken mirrors, wandering cats and all omens of popular superstition. Irrational? Yes. Childish? Certainly. Still ever-so-slightly worrying, even though you’re a post-Enlightenment adult with far more pressing cares, in the order of VAT returns and autumn colds and the impending nuclear apocalypse? Uh-huh.

And yet. Friday 13th is still… here. It’s a long-running horror franchise. It’s enough of a worry-factor for Western society that the date is said to wipe the best part of a billion dollars off the average American business day.

There have been lots of mooted origins for paraskevidekatriaphobia (the fear of this superstitious date), reaching back to the origins of Christianity, when there were 13 people passing the potatoes at the Last Supper. But the date is most keenly linked with the legendary organisation known as the Knights Templar: religious fanatics and armed defenders of the Holy Land during the medieval crusades.

That’s the Knights Templar, set up in around 1119 with its headquarters on the Temple Mount in Jerusalem – hence the name.

The Templars were the Kingsman agents of their time – a band of brothers set up to fight for the forces of good and save the world from evil. In practice, that meant escorting Christian pilgrims around crusader Jerusalem and slaughtering infidels everywhere from the mountains of Syria to the Nile Delta.

They also had a sideline in medieval financial services: tax collection, private banking, bailing out failing governments and managing huge estates of commercial and residential property.

Oh, you know: pretty hot on round-the-clock prayer, public displays of violence and expanding their financial hegemony around the world. But also pretty stylish.

The Templars had a clearly defined lookbook, laid down in their official Rule. First there was their iconic uniform of white or black robes emblazoned with a blood-red cross – as recognisable in their day as the Nike swoosh or Lacoste crocodile.

The Rule also made clear what was off limits. Pointy shoes were banned. So were lace-ups. Linen shirts were good. Fur was a no-no. Blankets were fine – if made from lambswool. Gloves were frowned upon for most.

Haircuts were to be short, so that each brother could be recognised “from the front and from behind” and while beards and moustaches were permitted, they had to be kept neatly trimmed. No moaning about any of the above was allowed. “If any brother out of pride or arrogance wishes to have a better and finer habit,” ran the Rule, “let him be given the worst.”

In 1307, the Templars were in trouble. The crusades were going badly and their wealth had attracted the attention of King Philip IV of France, who fancied a slice of it for himself. About 100 per cent, give or take. Actually, just take.

At dawn on Friday 13 October, 1307, royal agents turned up at every Templar property in the kingdom and presented arrest warrants falsely accusing the brothers of crimes against the church: spitting on the cross, denying Christ, worshiping false idols, kissing one another in lewd secret induction rituals (think: university rugby team initiation night) and sodomy.

The ensuing trials were a lot of medieval fake news: the allegations were repeated hundreds of times, until by 1312 they were so widely believed that Pope Clement V wound up the Templars for good. Two years later the last Templar grand master, Mr Jacques de Molay, was burned at the stake as a heretic.

So today, when you worry that you might lose your keys or miss the last train home on Friday 13th, be thankful that you’re not being burned to death as a falsely accused enemy of the Lord.

Since their own times, the Templars have been part of pop culture. They became interwoven with the original King Arthur stories 800 years before Mr Guy Ritchie got hold of them. They featured in Sir Walter Scott’s Ivanhoe and Mr Umberto Eco’s Foucault’s Pendulum, as well as in the adventures of Indiana Jones. And don’t forget their central role in Mr Dan Brown’s The Da Vinci Code. Later this year they will be the subject of Knightfall – a new big-budget drama series from History starring Mr Tom Cullen.

Hopefully nothing bad happens to you today – it’s only unlucky for some – but should you step on a rake or cross paths with a black cat, you now know whose name to use in vain.

The Sunday Times/New York Times bestseller The Templars: The Rise and Spectacular Fall of God’s Holy Warriors (Viking/Head of Zeus, $30/£25) by Mr Dan Jones is out now.

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