It was at Rome that young Giotto was to broaden and refine his art. He was called thither before the year 1300 to design the great mosaic of Christ walking on the Sea of Galilee beside the tempest-tossed boat of the Apostles. It stood over the inside cloister-portal of old St. Peter’s, and has been many times moved in the rebuilding of the church, and with each move restored, so that what we now see in the porch is entirely remade. From certain fragments of the old mosaic, and old sketch copies, Figure 12, we may judge that the Navicella, as the Italians loved to call it, was an elaborate composition of great dramatic power, the logical consummation of the experiments at Assisi. Our best version of the Navicella is Andrea Bonaiuti’s adaptation, Figure 31, for the vault of the Spanish Chapel, 1365. But Giotto was soon to renounce the facile method of diffuse and genial narrative in favor of a concise and massive style, akin to sculptured relief, and deeply influenced by the antique. The arches and the columns of Imperial Rome are teaching their silent lesson, the simple and noble forms of Cavallini and his nameless rivals show how painting may vie with sculpture in sense of mass and reality. With the problem of the representation of mass on a flat surface, Giotto wrestled eagerly and triumphantly. With a genius that few painters have equalled, he grasped the truth that the figure painter’s problem of representing space is chiefly that of emphatically suggesting mass. If you convince the eye of the tangibility of your objects, the mind will supply elbow room and air to breathe. It isn’t necessary to simulate a box, as the Sienese painters often did. The painter who can give a convincing sense of mass may handle accessories and perspective with the utmost freedom, according to the inner law of his design. The painter who thinks first of his space is in every way more bound to the smaller probabilities. Much thinking of this sort must have been done by Giotto before he worked out his new style at Padua. After his return from Rome, Giotto sojourned for a time in Florence, and in 1304 or thereabouts painted the gigantic Madonna formerly in the Trinità, Figure 13. It is impressive in mass, admirable in the intent expression of the attendant angels, rich in color, but the great figure is unhappily crowded by the canopy. Giotto is still a bit uncertain as to the rendering of space, and makes a good if unpleasing effort to suggest depth despite the limitations of a gold background. With all its nobility and tenderness, this is by no means so good a decoration as the great Madonna by Cimabue, Figure 4, which hangs nearby in the Uffizi.