The Knights Templar were formed after the first crusade, in the late Middle Ages, to capture the Holy Land (Palestine and Israel) from the Infidel1. They received the foundations of the ancient Temple of Solomon2 upon Mount Moriah in Jerusalem where they established their headquarters.
Their founder, Hugh de Payens, and his nine knights vowed to protect the overland path from the sea to the city of Jerusalem. For the first nine years of their existence however, they dug beneath the ancient temple, excavating an ancient network of tunnels. The Ark of the Covenant3 was supposed to be housed in this temple before the city was sacked by eastern invaders.
It's thought that the Knights Templar come across some ancient knowledge while they were excavating that may have originally come from Egypt or, as some have hypothesised, Atlantis.The knowledge was in the form of many things but most noticeably, to those in the Middle Ages, architecture. Gothic cathedrals sprung up throughout Europe in designs never seen before, one of the first being Chartres which employed flying buttresses. This is an architectural design feature which allowed for more space in the interior of churches and larger stained glass windows.
The Templars became extremely powerful over rather a short period of time, mostly thanks to the work of the priest named Bernard de Clairvaux (later St Bernard), who introduced them to Pope Honorius II, who eventually made them answerable to only him.
Upon their return to France, armed with what they had found, they grew strongly in number, gathering great quantities of gifts in lands and titles. Noblemen and peasants alike flocked to join the ranks of these knights who would then grant their own lands to the Order in the spirit of the brotherhood. Many noblemen who didn't want to join a crusade donated their lands to the cause in exchange for a quick passage to Heaven.
The Templars devised the modern banking system. Pilgrims could deposit their funds with the Templars in Europe, then by the use of a coded statement could take money from Templar strongholds upon the way to pay for their journey, for the path was fraught with peril. Upon arrival at the next destination point, the Templars would pay for the pilgrim's lodgings and re-code the chit, making the necessary deductions.
The Knights were always the first to enter a battle and the last to leave during the bloody crusades that saw the rise and fall of the Latin Kingdoms in the east of Tripoli, Antioch (Syria) and Jerusalem. The Church sang their praises and granted them many gifts for their service. They built many fine fortresses4, some of which still exist today.
After 200 years of occupying the Holy Land, they were ousted by the Saracens5 who proceeded to push them all the way back to Europe, via the Mediterranean islands of Cyprus and Malta.
Upon the conclusion of the West's attempted conquest of the Holy Land for Christendom, the Templars still earned great revenues from their lands, minus the cost to arm knights for crusades. They were exceedingly wealthy and had more funds than any European monarch. France was in great debt to the Templar organisation, and its king, Philip le Bel grew increasingly jealous of the wealth of the Knights. In 1307, upon the death of the then Pope, he brought many charges against the knights, including heresy. It is for this day Friday 13th was come to be known as unlucky, for that was the day that Philip arrested, simultaneously, all the Templars in France in a carefully planned operation. The Templars were alerted, and their fleet (which was greater than that of any nation) departed from France with all their wealth stowed on board, and was never again to be seen in Europe.
After the Pope officially disbanded the Knights Templar organisation, those remaining fled principally to Scotland and Portugal, two nations which refused to accept the Pope's authority at that time. Most of their confiscated wealth was redistributed to another religious order, the Hospitalliers of St John, thought to be linked with the Vatican.
The secrecy of the order has intrigued many, as inconclusive evidence points to the Knights Templar being in possession of holy artefacts such as the Holy Grail6, and the Ark of the Covenant and whatever else they may have found under the Temple of Solomon. Treasure hunters have tunnelled 200 feet deep into the recesses of Oak Island in search of what may be the final resting place of the Templar legacy. Many questions remain unanswered - did they discover America before Columbus (who flew the Templars' red cross on his sails) and take an instrumental part in the American independence? Did the Templars possess ancient knowledge, and did they find powerful sacred artefacts that caused their swift rise to power?
Only many more questions are raised in reply to these questions, and it's most unlikely we shall ever know the answers to any of them.