Urban seems to have procrastinated as long as he safely could, but, at length, at the tenth session, he produced Peter on the platform, clad as a pilgrim, and, after Peter had spoken, he proclaimed the war. Urban declined, however, to command the army. The only effective force which marched was a body of laymen, organized and led by laymen, who in 1099 carried Jerusalem by an ordinary assault. In Jerusalem they found the cross and the sepulchre, and with these relics as the foundation of their power, the laity began an experiment which lasted eighty-eight years, ending in 1187 with the battle of Tiberias. At Tiberias the infidels defeated the Christians, captured their king and their cross, and shortly afterward seized the tomb. If the eleventh-century mind had been as rigid as the Roman mind of the first century, mediæval civilization could hardly, after the collapse of the crusades, have failed to degenerate as Roman civilization degenerated after the defeat of Varus. Being more elastic, it began, under an increased tension, to develop new phases of thought. The effort was indeed prodigious and the absolute movement possibly slow, but a change of intellectual attitude may be detected almost contemporaneously with the fall of the Latin kingdom in Palestine. It is doubtless true that the thirteenth century was the century in which imaginative thought reached its highest brilliancy, when Albertus Magnus and Saint Thomas Aquinas taught, when Saint Francis and Saint Clara lived, and when Thomas of Celano wrote the _Dies Iræ_. It was then that Gothic architecture touched its climax in the cathedrals of Chartres and Amiens, of Bourges and of Paris; it was then also that Blanche of Castile ruled in France and that Saint Louis bought the crown of thorns, but it is equally true that the death of Saint Louis occurred in 1270, shortly after the thorough organization of the Inquisition by Innocent IV in 1252, and within two years or so of the production by Roger Bacon of his _Opus Majus_. The establishment of the Inquisition is decisive, because it proves that sceptical thought had been spread far enough to goad the Church to general and systematic repression, while the _Opus Majus_ is a scientific exposition of the method by which the sceptical mind is trained.