The columns of the nave are all of antique marble, the ruins of a Roman temple to Ceres at Pisa; some are of cipollino, others Oriental granite, one is of fluted white Greek marble. The capitals are mostly antique and classical, though a few show the hand of the early Comacine in their straight upstanding volutes. The ingenuity of the _Magistri_ in making use of old material is shown in the various devices by which these columns are adapted. Where they are too short the base is raised on two pedestals; where too small for the massive pillar, a wide abacus is placed on the top to support the arch. One of the columns which support the altar is made long enough by a base made of an antique carved capital reversed beneath it. We have a distinct sign of the Comacines in a stone let into the wall near the door, and which evidently formed part of the ancient architrave. It is carved in an intricate interlaced knot. I shall speak in the chapter on Comacine painting, of the frescoes in the nave, which are unique of their kind, and of deep interest to the Art historian. [Illustration: EXTERIOR OF SAN PIERO A GRADO, PISA, 8TH CENTURY. _page 101._] These churches of the Carlovingian era in Italy cannot be documentally proved to have been at all connected with Charlemagne himself, except that he sent the _Magistri Comacini_ to Rome, at Pope Adrian's request. The same cannot be said of the great church of Aix-la-Chapelle, with which his name must be for ever united, but which is certainly not entirely unconnected with this Lombard Guild. Where history gives no precise information, and where authors, ancient and modern, fail to fix the precise era of this important work, it is of course impossible to say who was the architect. We can only judge by the style, and by inferences drawn from previous works of the same style. First, as to the few facts we are able to gain: Eginbertus, a Lombard, the biographer of Charlemagne, in his _De vita et gestis Caroli Magni_, Capit. 26, tells us that Charlemagne "built the Basilica of Aquisgrana of wonderful beauty, and adorned it with much gold, silver lamps, and with gates and doors of bronze. For this construction, not being able elsewhere to find columns and marble, he provided that they should be brought from Rome and Ravenna." This fact, of a want of proper material in France, would seem to imply that skilled workmen to build in stone must have been imported with the material. It is difficult, or indeed impossible, to prove that French workmen were equal to the occasion, by showing other contemporary works in France. Any churches they may have then had, have long since perished, for at that date they were usually built of wood; another argument that France could not have supplied accomplished architects in stone.