Invasions and wholesale conflagrations had impressed on the mediæval mind the necessity of a church roof more durable than wood, but a masonry vault over a wide space was a constructive feat too difficult to be achieved immediately. In fact, up to the very end of the XI century, though the builders had succeeded in vaulting with stone the crypt, the apse, and the side aisles, they continued generally to cover the wide central vessel in wood. However, the fecund idea was at work. From the time that it took possession of their imagination, to the day when Gothic, its fulfillment, was clearly enunciated, there was over a century of continuous effort--roughly speaking, from the year 1000 to the memorable day in 1144 when was dedicated the first truly Gothic monument of considerable size--the abbey church of St. Denis. Within that energetic span of years is embraced the Romanesque architecture of France.[9] The monk, Raoul Glaber, wrote an account of the rebirth of architecture after the year 1000. It has been quoted to weariness, but is none the less a valuable contemporary record. The whole earth, he says, as of one accord seemed to throw off its tatters of old age and to reclothe itself in a white mantle of churches. The monastery in which lived monk Raoul, St. Bénigne, at Dijon, was one of the first to inaugurate the new century, and its present crypt dates from the year 1001. Soon after 1017 the monks of Mont-Saint-Michel, in the far corner of Normandy, began a new church, to which belonged part of the present nave. At Chartres, Bishop Fulbert undertook to rebuild his cathedral after the fire of 1020, and the vast crypt which to-day astonishes every beholder was his work. The chronicler, Raoul Glaber, lived under the rule of the most powerful monastic brotherhood ever organized, Benedictine Cluny, embracing several thousand houses scattered over Europe. Founded in 910, during the darkest years of the Middle Ages, Cluny kept alive the light of learning and art, "the solitary torchbearer that passed on the flame from the spent glow of Charlemagne to the Gothic rekindling." Her monks were the pioneers of civilization. Cluny beat back barbarism with a pertinacity that should make hers an honored name in history. So established was her reputation as a civilizer that William the Conqueror wrote to the great Abbot Hugues, to beg from him Cluny monks for England, saying that he would pay their weight in bullion.