The struggle for a satisfactory stone roof was pursued tenaciously. Many a clearstory wall was thrust apart by the vaulting's pressure. Thus the abbey church of Bec, finished in the 'forties of the XI century, was reconstructed in the 'fifties, and three times, again, had to be rebuilt. No failure could daunt the courage of those old monastic builders. Already inherent in the newly amalgamated race was the creative genius of France. Perseverance and courage were to have their reward. The theory long taught in the École des Chartes was that in the first part of the XI century, among a number of rural churches in the royal domain, there gradually came into use the member which was to revolutionize the science of building. The idea did not spring from one brain; it was a collective, not an individual, triumph. When, under some groin vault, no doubt at first to reinforce it, some obscure mason constructed the earliest intersecting stone ribs, the first step in Gothic architecture had been taken.[11] From that essential organ, the other characteristics of Gothic art were deduced: flying buttress, slender piers, expanse of windows. In a Gothic vault the infilling, or web, rested elastically on the diagonal ribs. As the load of the stone roof was thus concentrated at fixed junctures, it was necessary to reinforce only those given points. Buttresses became intermittent. All the disintegrating force of the heavy vaulting was gathered on the diagonally crossing arches. An arch never sleeps, said the old Arab proverb. Let us then, said the mediæval architect, set a guard on it that also never sleeps; and from that idea he proceeded to develop the greatest architecture of all times. The force of expansion was counteracted by a proportionate force of compression. By means of a framework made up of vault ribs, of piers, of buttresses, and flying buttresses, the edifice became a living skeleton. The walls between the active members, when relieved of their load, served merely as screen inclosures and could be carved into fragile beauty and hung with transparent tapestries of colored glass. Because the flying buttress transmitted a large part of the vault's pressure to the exterior buttress piles, the piers within the church could be lessened in diameter, and greater capacity be given to the interior.