Cluny formed the savants who made the XII century memorable. Her fertile seed provided Europe with doctors, ambassadors, bishops, and popes. Gregory VII had passed through her discipline, and in his giant task of reform, it was from Abbot Hugues that he solicited monks of Cluny. Urban II, who set in motion the First Crusade, had been a monk in the great Burgundian house. It is interesting to note that a generation of reforming pontiffs accompanied the expansion of the Romanesque movement. This would seem to contradict the notion, which many hold, that the clergy profits by keeping the people in superstitious ignorance. It is when religion is purified of its dross that man's respiritualized faith out-flows in generous donations to the Church. St. Benedict had taught his sons that work as well as prayer was a part of salvation. The monks of Cluny fostered agriculture, thus taking away its stigma as serf's work. Thierry speaks of the mediæval monastery as a model farm. In Cluny craftsmen of every kind were trained; its school of music was noted, and along the roads, as they traveled, the monks from Burgundy sang canticles. But the art of arts for Cluny was that of the builder, the supreme art that takes into its service all the others, to lead them to the glorification of God's house. When, in bands of twelve, the monks of Cluny set out to colonize in Spain, in Germany, in Italy, in Poland, everywhere they carried with them the tool as well as the Book. As a rule they conformed in each province to the local building traditions. There was never a distinct Cluny school of Romanesque architecture. By the end of the XI century the main provincial centers of France had each evolved its own special building characteristics. French Romanesque architecture has been divided into some six or seven regional schools--those of Normandy, Burgundy, Auvergne, Poitou, Languedoc, Provence, and a minor school, the Franco-Picard.[10] In their efforts to protect their churches by masonry roofs, these various regional schools made use of the barrel vault or the groin vault. The latter was found too insecure to span a wide space. Now, the thrust of a barrel vault was exerted along the whole length of the wall, which necessitated a continuous abutment--in other words, an enormously thick wall. Only small windows could be opened. Since the Romanesque architect had the ambition to light his church well, and not to encumber his floor surface by clumsy piers, a barrel vaulting could be but a temporary solution of the main problem.