To the historical scholar this period is unsurpassed in importance by any, if we except the days of the birth of Christianity. The age of the crusades covers the eleventh and twelfth centuries. For two hundred years, to use the vigorous language of the Greek princess Anna Comnena, who witnessed the first crusade, “Europe was loosened from its foundations and hurled against Asia.” As an Alpine glacier presses down into the valley, only to melt away at the summer line, yet with renewed snows repeals the fatal experiment from year to year, so seven times Western Christendom replenished its mighty armaments, to see them destroyed at the border-land of Oriental conquest. To define the causes of these vast movements is a task which both tempts and tantalizes the historian. It is surely unlearned to ascribe even the first crusade to the sole influence of any man, though he were an Urban II. and wielded the temporal and spiritual authority of the Papacy in its most puissant days. It is puerile to say, as Michaud does, speaking of Peter the Hermit, “The glory of delivering Jerusalem belongs to a single pilgrim, possessed of no other power than the influence of his character and genius.” It is equally uncritical, if not blasphemous, to attribute these most unfortunate and ill-timed ventures to the Almighty, as the same writer does in these words: “No power on earth could have produced such a great revolution. It only belonged to Him whose will gives birth to and disperses tempests to throw all at once into human hearts that enthusiasm which silenced all other passions and drew on the multitude as if by an invisible power.” To even approximate an understanding of this subject, one must first become familiar with the great racial movements which culminated in that age; must be able to estimate the tendencies of society at a time when it knew not the forces which were struggling within itself; must penetrate the policies of statesmen and ecclesiastics who veiled their ambition under the self-delusion that they were serving God or their fellow-men; and, besides all this, he must gauge the passions and habits of common people, their ignorance and superstition, if not the true heavenly ardor which led them to offer themselves as fuel for the most stupendous human sacrifice the world has known. Were one thus equipped with information, one’s philosophical judgment might still be baffled with the inquiry, What was the chief cause of the crusades? An observation of Dean Milman is especially applicable to this subject: “When all the motives which stir the human mind and heart, the most impulsive passion and the profoundest policy, conspire together, it is impossible to discover which is the dominant influence in guiding to a certain course of action.” The mighty tide of events we are to consider was not unlike a vast river which sweeps through many lands and has many tributary streams, some of whose sources are hidden in the depth of the unexplored wilderness.