The choir, however, was finished about 1270, and stood for several years. But dislocations then declared themselves. The forces so elaborately balanced lost their equilibrium, and on the 29th November 1284 the vault fell, dragging down with it the flying buttresses, and carrying havoc through the rest of the building. In the reconstruction which followed it was thought imperative to double the points of support in the arcades both of the main and side aisles, and to reinforce the flying buttresses by iron chains. [Illustration: 51. BEAUVAIS CATHEDRAL. TRANSVERSE SECTION] During the thirteenth century a number of cathedrals were raised all over Europe on the model of the great buildings of Northern France, and more especially of Amiens, which seems to have roused a great enthusiasm; these were, however, of far more modest dimensions. They had neither the exaggerated height nor the structural audacities of their exemplars. Few of these churches and cathedrals, the reconstruction of which on the new system generally began with the choir, which was added to the primitive nave, were completed by those who initiated their erection. The most highly favoured in this respect were finished in the course of the fourteenth century; but in the greater number of cases the work dragged slowly on, and reached its end some two centuries after its inauguration. Reconstructive undertakings were constantly impeded by wars or social convulsions, which either hampered or entirely cut off the resources of bishops and architects, their promoters. Such interruptions were of great service to modern archæological study, offering as they do distinct evidence of the various transformations which were successively accomplished from the so-called Romanesque period to the Gothic. [Illustration: 49. BEAUVAIS CATHEDRAL. APSE] [Illustration: 50. BEAUVAIS CATHEDRAL. NORTH FRONT] [Illustration: 51. BEAUVAIS CATHEDRAL. TRANSVERSE SECTION] [Illustration: 52. CHARTRES CATHEDRAL. ROSE WINDOW OF NORTH TRANSEPT] The majority of these great buildings, which show traces of the vicissitudes through which they passed, bear a strong likeness to each other, and vary only in detail, according to the skill of their constructors. The peculiar interest of Chartres centres in its remarkable statuary; it has, however, other features which command attention, such as the rose window of the north, transept and the design of the flying buttresses. These consist of three arches, one above the other, the two lower ones being connected by colonnettes, radiating from a centre, so that the lower arch is related to the upper, as the nave of a wheel is to the felloes, the colonnettes forming the spokes.