Treize69 is right.
Short version, after many crusades to Jerusalem the royal vaults across Europe were nearly empty. This lead to massive depressions, etc. The Templars were a knightly order of warriror monks, of sorts. They were officially ordained by the Pope and were tasked with guardian Christian pilgrims as they journed to and from Jerusalem. Part of joining the Knights Templar was giving all of your earthly possessions to the order, taking vows and living with the sword and poverty.
Fact, our modern day system of writing checks in exchange of currency came from Templar castles located all over Europe. You could deposit gold in one Templar castle, say in Scotland. They would give you a receipt that was encrypted. You could travel to Italy, take the receipt to a Templar castle they would give you the gold, minus interest and handling fees. Prior to this one had to travel with all of their gold, or risk impoverishment. Over a few centuries the Templars became wealthier then any King, kingdom or the Catholic Church. In fact, those who wanted to join the order could not do so if they were indebted at all. Only those with money, or atleast no debt.
Fast forward to 1307, the King of France, desperate for cash struck a deal with the Pope. He made claims against the head of the Templars and the order in general. There was a secret decree to arrest all of these knights of god. Of course being a military order the arrest of these warrior knights was not to be taken lightly. Secretly the King of France sent orders to all his forces directing them to arrest all Templars throughout the kingdom. Of course they did not have email, phones, etc so the trick was to coordinate the arrest kingdom wide without the aide of modern communications. How do you issue such a broad decree without the Knights learning about it and responding? It was simple.
The king issued orders sealed in wax with the decree for arrest in the inside. On the outside was the simple direction, open and obey on Friday the 13th. So on that day, at dawn all through France the seal was broken, troops mounted and Templars arrested. Many escaped to other parts of Europe, with the last stronghold being in Scotland. Imagine the general populace and their reaction as they saw this play out. From that time on Friday the 13th was an unlucky day to be guarded against.
I did this research for my senior paper in college. Very interesting. And this is only the beginning of the story.
Boo