XI. There is another very curious instance of distortion above the central door of the west front. All the intervals between the seven arches are filled with black marble, each containing in its centre a white parallelogram filled with animal mosaics, and the whole surmounted by a broad white band, which, generally, does not touch the parallelogram below. But the parallelogram on the north of the central arch has been forced into an oblique position, and touches the white band; and, as if the architect was determined to show that he did not care whether it did or not, the white band suddenly gets thicker at that place, and remains so over the two next arches. And these differences are the more curious because the workmanship of them all is most finished and masterly, and the distorted stones are fitted with as much neatness as if they tallied to a hair's breadth. There is no look of slurring or blundering about it; it is all coolly filled in, as if the builder had no sense of anything being wrong or extraordinary: I only wish we had a little of his impudence. XII. Still, the reader will say that all these variations are probably dependent more on the bad foundation than on the architect's feeling. Not so the exquisite delicacies of change in the proportions and dimensions of the apparently symmetrical arcades of the west front. It will be remembered that I said the tower of Pisa was the only ugly tower in Italy, because its tiers were equal, or nearly so, in height; a fault this, so contrary to the spirit of the builders of the time, that it can be considered only as an unlucky caprice. Perhaps the general aspect of the west front of the cathedral may then have occurred to the reader's mind, as seemingly another contradiction of the rule I had advanced. It would not have been so, however, even had its four upper arcades been actually equal; as they are subordinated to the great seven-arched lower story, in the manner before noticed respecting the spire of Salisbury, and as is actually the case in the Duomo of Lucca and Tower of Pistoja. But the Pisan front is far more subtly proportioned. Not one of its four arcades is of like height with another. The highest is the third, counting upwards; and they diminish in nearly arithmetical proportion alternately; in the order 3rd, 1st, 2nd, 4th. The inequalities in their arches are not less remarkable: they at first strike the eye as all equal; but there is a grace about them which equality never obtained: on closer observation, it is perceived that in the first row of nineteen arches, eighteen are equal, and the central one larger than the rest; in the second arcade, the nine central arches stand over the nine below, having, like them, the ninth central one largest. But on their flanks, where is the slope of the shoulder-like pediment, the arches vanish, and a wedge-shaped frieze takes their place, tapering outwards, in order to allow the columns to be carried to the extremity of the pediment; and