As we wander about this glorious fabric, with its hundreds of statues,[130] its blazing windows, its vaulted roof which hangs its massive weight of stone so safely above our heads, all attempts at detailed description become futile. Let them be left for other books and other moods. Later generations doubtless will record at great length that about the middle of the twelfth century a great activity in church building, as a surpassing work of Christian piety, began to manifest itself especially in northern France. This activity was not to spend itself for more than a hundred years.[131] It absorbed much of the best thought and energy of the time. In addition, it developed a genuinely new type of architecture, a real innovation upon those models traceable back to the pagan Greek. We come to the reign of the pointed arch which adapts itself to endless curves and varieties. We have, too, the grouped columns which uphold the groins of the lofty vaulting, their members radiating outward like the boughs of a stately forest. These columns and piers can be made amazingly light, thanks to the daring use of flying buttresses, an invention not merely of great utility, but of great beauty. Thanks also to these grouped pillars, groins, and buttresses, the walls between the bays (intervals between the columns) are in no wise needed to uphold the roof of stone; and as a result these bays can be filled up with thin curtain walls crowned above with enormous windows which are filled with a delicate tracery and a stained glass that throws down upon the pavement of the church all the rainbow tints of heaven. Each bay is likely to contain a separate chapel or at least an altar to some particular saint. Over the portal, where the main entrance gives access to the long nave, radiates the mighty rose window, the final triumph of the glass and tracery. And so through all the vast structure--huge in proportions, yet, as it were, a harmonious mass of fair carving and jewel work, until (even as says Holy Writ) "the whole body fitly joined together, and compacted by that which every joint supplyeth, according to the effectual working in every part, maketh increase of the body unto the edifying of itself in love." [Sidenote: Magnificent Dimensions of Cathedrals] So the apostle of the making of a Christian man, so, too, of the making of the august church. And after saying this, what profit to add that this cathedral has a length of about four hundred feet, that the ceiling of the nave rises at least one hundred feet above the pavement, that the rose window is nearly forty feet in diameter, that the higher tower is much more than two hundred?[132] Numbers are for sordid traffic, they are not for a work wrought out of a passionate love of man toward God.