Crusade historian Christopher Tyerman once wrote that:
The Templars occupy a prominent place in the pantheon of Alternative History of the ‘what they have tried to conceal from us’ genre, championed by obsessive, swivel-eyed anoraks and conspiracy theorists allied to cool money sharks bent on the commercial exploitation of public credulity.
Now I wouldn’t put it quite that way, but it’s true: like the Bermuda Triangle, the lost continent of Atlantis, and the Nazca Lines, the Templars do tend to attract a good deal of Speculation. The Templars, or more formally “The Poor Fellow-Soldiers of Christ and of the Temple of Solomon,” were founded as a religious order in 1119 in the Crusader kingdom of Jerusalem. Like the crusading movement itself, they represented “a fusion of Christian and military practice” – that is, the members took vows of poverty, chastity, and obedience, but instead of praying eight times a day and copying out manuscripts like monks, they practiced horsemanship, guarded pilgrims to the Holy Land, and fought Muslims as they needed to, like knights. (This is definitely a novelty – prior to the late eleventh century the Church did not like knighthood much, but after numerous unsuccessful attempts at regulating it, the Church threw in the towel, and gave it their blessing – but only if the knights exercised their craft far from Europe, and against non-Christians. Thus were they allowed to organize themselves into religious orders.) What attracts everyone’s attention is the Templars’ sordid end: in 1312, King Philip IV of France accused them of heresy, tortured confessions out of the leadership, and prevailed on Pope Clement V to dissolve the order, after which many of them were burned at the stake. But some of the Templars, it is alleged, escaped and “went underground,” later to emerge as the Freemasons. Some of them even sailed to the New World before Columbus, which is why the fifteenth-century Rosslyn Chapel in Scotland, built by supposed crypto-Templar William Sinclair, features carvings of new world corn. One author claims they buried treasure in the Oak Island Money Pit off Nova Scotia. A student of mine once lent me a book suggesting that the Shroud of Turin actually depicts an image, not of Jesus, but of the martyred Templar Grand Master Jacques de Molay. A character in Dan Brown’s Da Vinci Code asserts that the Templars, while in the Holy Land, had uncovered evidence that the Papacy was a con job, and that the leadership of the true Church belonged to the descendants of Jesus Christ and Mary Magdalene – which is why the Pope was so keen to eradicate them.
I tell my students that history is interesting enough without concocting such theories. The real history of the Templars touches on several late-medieval themes – among them the rising power of the king of France (at the expense of the papacy), and the desire to find a scapegoat for the loss of the Holy Land (Acre, the last Christian stronghold there, had fallen in 1291). But what it touches on the most is the money one could make as a result of the medieval commercial revolution – and the envy this provoked in others. The Templars were not just active in the Holy Land – they had chapters throughout Western Christendom (their churches were usually round, and you can visit one in London). Templars got into long-distance banking – and made a fortune, so much so that their formal title of “Poor Knights,” and their seal showing two knights riding a single horse, became ironic.

Wikipedia.
A BBC article, which my friend Chris Berard points me to, explores this history in greater detail. Author Tim Harford claims that they “invented modern banking.”
The Templars dedicated themselves to the defence of Christian pilgrims to Jerusalem. The city had been captured by the first crusade in 1099 and pilgrims began to stream in, travelling thousands of miles across Europe.
Those pilgrims needed to somehow fund months of food and transport and accommodation, yet avoid carrying huge sums of cash around, because that would have made them a target for robbers.
Fortunately, the Templars had that covered. A pilgrim could leave his cash at Temple Church in London, and withdraw it in Jerusalem. Instead of carrying money, he would carry a letter of credit. The Knights Templar were the Western Union of the crusades.
We don’t actually know how the Templars made this system work and protected themselves against fraud. Was there a secret code verifying the document and the traveller’s identity?
They did more than this, however:
Templars were much closer to a private bank – albeit one owned by the Pope, allied to kings and princes across Europe, and run by a partnership of monks sworn to poverty.
The Knights Templar did much more than transferring money across long distances.
As William Goetzmann describes in his book Money Changes Everything, they provided a range of recognisably modern financial services.
If you wanted to buy a nice island off the west coast of France – as King Henry III of England did in the 1200s with the island of Oleron, north-west of Bordeaux – the Templars could broker the deal.
Henry III paid £200 a year for five years to the Temple in London, then when his men took possession of the island, the Templars made sure that the seller got paid.
And in the 1200s, the Crown Jewels were kept at the Temple as security on a loan, the Templars operating as a very high-end pawn broker.
Harford goes on to say that Philip IV owed money to the Templars, and didn’t like how they operated beyond his control, and so contrived to dissolve them. But I can’t help but think there was even more at stake here. Lester Little’s Religious Poverty and the Profit Economy in Medieval Europe (1983) talks about how money made people very anxious in the Middle Ages, especially the “money from nothing” that one could get from currency exchange, lending at interest, or taking advantage of scarcity to sell at a premium. Charging more money than the “just price” for something was uncharitable and un-Christian, and if you made any extra-normal profits at all the only way to expiate your sin would be to give it all to the Church. (This helps to explain all those elaborate late medieval “wool churches” in East Anglia, and it also helps to explain the increased anti-Semitism of the High Middle Ages – Jews were increasingly shut out of various professions, leaving them in the role of the hated money lender.) It’s true that the Templars were themselves a church organization, but I suspect that just made it worse.
As unfair as their end was, however, it happened. “Templar” groups today are somewhat disreputable – at least, they have no institutional continuity with their medieval namesake. If you’re interested in joining a crusading order, try the Hospitallers, the Templars’ main rivals in the Middle Ages, who do enjoy continuity and who are thus much classier.