The medieval crusading period threw up literally dozens of military orders–knights sworn to lead religious lives as well as fighting the enemies of Christ.

We never hear about the mysteries of the Hospitallers. Or the secret bloodline of Jesus guarded by the Teutonic Order. Or strange sites and caves dug by the Order of Calatrava or the Sword Brothers of Livonia.

Yet for centuries the Knights Templar have obsessed and fascinated us.

From as early as the 13th century the Templars have been popping up in popular culture. Around 1200 A.D. they appeared in a wildly popular German edition of the legends of King Arthur, in which Templar-like knights were portrayed as guardians of a mysterious object known as the Holy Grail.

At that point the Knights Templar, established in Jerusalem in 1119 after the First Crusade, were very much alive and kicking. In fact, in 1200 they were still manning castles, guarding pilgrims and fighting on the front line against Muslim armies in Syria, Egypt and Palestine, while managing a massive property empire across Europe, from Ireland to Cyprus.

READ MORE: The Knights Templar: The Rise and Spectacular Fall of God's Holy Warriors

They had earned such a reputation as fearsome warriors and devout Christians that it was only natural for writers to romanticize them. It’s not too different from Hollywood’s obsession today with spies. We know that James Bond and Jason Bourne aren’t exactly models for how real MI6 and CIA assets exist in reality. But we love to go along with the fantasy, because it’s entertaining.

The beginnings of Templar mythology are much the same. These were the supermen of the Middle Ages—why wouldn’t you tell stories about their superhuman deeds?

Yet today, in the 21st century, we are still obsessed with the Templars. The Templars are rich subject matter for books, films and high-end TV dramas, from Dan Brown’s Da Vinci Code to HISTORY’s own Templar series "Knightfall." Generation after generation, from Walter Scott’s 19th-century romance Ivanhoe to Umberto Eco’s 1988 novel Foucault’s Pendulum to the video game franchise "Assassin’s Creed," the Templars are portrayed as a strange, often shadowy and sometimes downright evil organization, deathless and self-interested, guarding secrets and treasure, and out to control the world.

Outside entertainment they have been linked (speciously) with the origins of freemasonry, and have provided a sinister model for other, far less well-meaning groups. There is a Mexican drug cartel which calls itself Los Caballeros Templarios, directly modeling itself on the Knights of the Temple. The Norwegian mass murderer and far-right terrorist Anders Breivik claimed to be a modern Templar.

That’s an incredible rise and longevity for a medieval military order, even one that was as famous in its time as the Templars.

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Part of the reason for the enduring mystique is the sheer range of business the Templars transacted. The order began as bodyguards, protecting pilgrims on the roads around Jerusalem in the 12th century. They developed into an elite military force.

In the 13th century they added international banking services to their range of skills and took over accountancy services for royal governments. They were largely tax exempt and protected by the authority of the Pope. As an organization they could rival whole countries for wealth and military capability.

Roll all that together and you have an organization that is a bit like a cross between Blackwater, the Navy SEALS, Deloitte and Google. With medieval religious fanaticism to boot. That’s a potent cocktail to keep us interested in them today.

More important than any of that, though, is the nature of the Templars’ fall.

By the start of the 14th century the Crusades were badly faltering. Western Christians had been entirely kicked out of the Holy Land, with their last major bastion in the city of Acre being seized in 1291.

READ MORE: Medieval Times: A Timeline of Top Templar Moments

The Templars took a heavy share of the blame for that, some of it fair, much of it very unfair. One of their severest critics was Philip IV, king of France, who also wished to help himself to the order’s massive wealth in order to stabilize a badly mismanaged French economy.

On 1307 Philip’s agents rounded up all the Templars in France. They were tortured, tried and accused of grotesque heresy, blasphemy and sexual crimes. The charges were trumped up and blatantly false–medieval fake news–but Philip was backed by a weak, French Pope, Clement V, and he managed to have the order disbanded–not only in France but across the whole of Europe. The order’s leaders, including its last master, James of Molay, were burned to death in Paris in 1314.

The dark accusations Philip IV made against the order were almost entirely bogus, but they nevertheless created an image of a dirty organization with secrets that would shock the world—an idea that has never really gone away. And the extraordinary swiftness with which the Templars were shut down and rolled up has led many people to doubt that they could really have disappeared, and concoct unlikely but exciting survival myths.

Roll all that together with everything else that we know about the real Templars, and it’s no wonder they have been the subject of wonder and speculation since their own times–and why they will continue to be for generations to come.