The Knights Templar were a Militant Monastic order, that is, by the time they were chartered they had one and only one purpose, to liberate the holy land from "the infidel", (sic: Muslims). As many persons have stated, they were avid archeologists, and from humble beginnings, after a period of digging under the remains of Solomon's Temple emerged wealthy and powerful.
The organization of the order was quite sophisticated, in that there were a number of classes of members, both of the Knightly and peasant classes. The bulk of these members were military knight/monks, who had two avocations, literally: praying and fighting. Overseeing these individuals were the literate/clerical arm which was responsible for the administration of the various aspects of the order. To be a member of either of these groups, one had to be of the Knightly class. This was the basis of their allegedly incredible wealth. Pesants who entered the order became farm labourers and foot soldiers, or Sargents at Arms.
Typically, the persons who entered the order were the second sons of the European nobility, who were not in a position to inherit their family's lands and fortunes. Once a vow of poverty was taken, all of the individuals property became the property of the order. Curiously, if a member became eligible to inherit his family's fortune through the death of an elder sibling, that property passed to the order. Between this, the entry tithe, and grants paid by noble families over the two centuries or so of its existence, the order acquired substantial European holdings.
As their size and influence grew, and as the political climate in Europe changed, so the Templars changed. Eventually, as time went on, they lost the Holy Land, and their Mediteranean holdings. As a result, they became an army with out purpose, answerable only to the Pope.
Their downfall was a function of the changing political climate in Europe. The Papacy was unable to convince European princes to crusade on its behalf, and governments, chiefly Phillip II of France, were wary of their power, both military and financial. By the end of the fourteenth century, the Knights Templar had lost their raison d'etre, and were a liability to the Pope who could not afford them, and to Phillip II who owed them great sums of money.
There is great popular curiosity about the whereabouts of the Templar navy and fortune. It is apparent that the Templar Masters themselves had some forewarning of the consequences of the Paris meeting, on account of the disappearance of the Templar navy, and empty coffers. Where they went is a matter of speculation, that has kept scholars and enthusiasts occupied for years.