Knights of Templar
The Knights of Templar were formed in 1118 and were known as the Poor Knights of Christ. The Knights of Templar are mentioned throughout The Da Vinci Code because they are associated with the Holy Grail.
The Church, at one point in time, were in favor of the Knights. They have numerous castles throughout the Holy Land that served for both military campaigns and as chapels.
The Knights set up one of the first international banking system. The wealthy knights and landowners could leave their wealth in safe hands - for free. Eventually, they owned a large amount of property in Europe and the Middle East.
They gained a reputation for being very secretive and obsessed with rituals. But, unfortunately, their downfall came on Friday, October 13, 1307. This is where the idea of bad luck coming on Friday the 13th started. A large number of Knights in France were arrested by Philip the Fair of France. Many were tortured and killed, while others had to admit to practicing heretical acts. Pope Clement V. dissolved the order.
There is an idea that before they were dissolved, they found a treasure beneath the Temple Mount. Some think that they may have even found the Holy Grail. But, it's not likely that we will ever know if they had a treasure and if it was the Holy Grail.