The great contest of the thirteenth century between the Empire and the Holy See for the mastery of the world derived its origin from the barbarian occupation of Italy. The imperial dignity of the Cæsars embodied, as is well known, not only its supreme exercise, but the prestige and the mysterious power which attached to the place of Pontifex Maximus, the prototype of the Papacy. That power had been solemnly confirmed, and materially enlarged, by the ambition and politic measures of Constantine. The occasional employment of the Bishop of Rome as arbiter of the differences between the Sees of Constantinople and Alexandria had magnified the importance and insensibly extended the jurisdiction of his office. Aspiring prelates, who held their court on the banks of the classic Tiber, in sight of the stupendous memorials of ancient civilization, soon began to arrogate to themselves a preponderance in the determination of secular matters to which their comparatively obscure predecessors had advanced no claim. The texts of Scripture were invoked and interpreted to confirm their pretensions. In addition to the alleged vicarious sovereignty vested in them by the traditional choice of the Saviour, they asserted that the privileges and authority enjoyed by the Pontifex Maximus were theirs by the right of inheritance. They insisted, moreover, that as celestial matters were of far greater importance to mankind than any connected with the affairs of a transitory life, the sacredness of their exalted position conferred extraordinary prerogatives, and that the imperial power was subordinate to, and, under some circumstances, actually merged into, the pontifical dignity. By thus shrewdly taking advantage of every circumstance which could either strengthen its influence or extend its jurisdiction, the Holy See subjected to its tyrannical and irresponsible sway a far more extensive and populous territory than had ever paid reluctant tribute to the masters of imperial Rome. Excommunication, anathema, and interdict, the means by which this tremendous authority was enforced, were moral instruments which appealed with irresistible force to the fears of a superstitious age.