The papacy, next to Christianity, is the great fact of the modern world. Of the two, the former, unhappily, has proved, in some respects, to be the more powerful spring in human affairs, and has acted the more public part on the stage of the world. To fully trace the rise and development of this stupendous system is to write a history of Western Europe. On so wide a field of investigation, neither our time, nor our limits, permit us to enter. Let it suffice that we indicate, in general terms, the main causes that contributed to the rise of this tremendous power.