The vaulting of the choir differs from that of the nave, but the difference is one rather of detail than of principle. We have already said much about the external buttress system by which this splendid roof is sustained. Internally this vaulting rises from slender shafts springing from the capitals of the great cylindrical columns constituting the main arcade of the ground story. The piers at Paris are ill adjusted to the vaults, a feature which has resulted in an immense amount of learned discussion. They were obviously intended for quadripartite vaulting. It seems probable that suddenly, for a reason which we are not now in a position to appreciate, the quadripartite form was abandoned in favour of the sexpartite form actually adopted. Students of this subject are advised to refer to pp. 114-15 of the second edition of Mr. Moore’s book, where the differences between the vaulting imposts of the nave and choir are discussed and delineated. They may profitably compare this with M. Viollet-le-Duc’s _Construction_ (p. 164). M. Viollet-le-Duc, it may be added, suggests that the necessities of the sexpartite system were provided for by the monolithic shafts grouped round every other pier in the arcade dividing the aisles. [Illustration: CAPITAL IN THE NAVE. _From Viollet-le-Duc._] The somewhat heavy character of the great cylindrical piers which divide the nave from the aisles is largely redeemed by the beautiful carving with which the capitals are ornamented. The plants which the sculptors have conventionalised are those commonly found in the fields adjacent to Paris. These ornate capitals are genuinely Gothic in feeling, and have nothing in common with those which crown the piers of our Anglo-Norman (Romanesque) cathedrals. Again, the plinths of the columns are utterly unlike the simple and massive bases on which the round columns of our older churches most often rest. We have already alluded to the ill-adaptation of these piers and their capitals to the sexpartite form of vaulting employed. In the case of the most westerly piers of the main arcade an attempt seems to have been made--with no great success, as it appears to me--to minimise the illogical effect of the vaulting imposts. The result has been the emphasis of that very want of congruity which it was sought to remedy. It would be difficult to find a less satisfactory arrangement than that which obtains in the pier and capital delineated in our illustration, where four smaller cylinders are attached to the main one. Here, not merely is the pier itself rendered unwieldy by its satellites, but the capital loses all symmetry owing to the interposition of the small capitals which crown those satellites. It will be noticed that the arches of the main arcade are by no means uniform. Thus we have a wide arch adjacent to an extremely narrow one, while the builders of the period did not hesitate to make use of a round arch where they found that form more convenient.