Greek reliefs had always been represented as if against a tangible background, at first practically in two planes only, and then in Hellenistic times in truer perspective, but invariably against a background of some kind. Roman art, on the other hand, in its more developed reliefs like those on the Arch of Titus,[125] eliminates the idea of background and regards the wall on which the reliefs are placed as nonexistent. The reliefs are intended to give the illusion of free sculpture, as if they were standing in the round against a background of the sky. A much greater depth must, therefore, enter into the principle of perspective. Just as in the bronze reliefs of the Florentine Baptistery Ghiberti used the principle of no background and attempted to show a whole countryside behind his figures as if the relief were a picture, so the artist of the reliefs of the Arch of Titus uses a strongly diminishing perspective and a pronounced foreshortening of his figures to produce this same effect of free sculpture. In Greek sculpture of the Hellenistic age it is true to say that the depth of the background has been greatly increased. This is visible even as early as the Telephos frieze. But it would be hard to point to a Greek relief in which the effect was wholly pictorial and the idea of the background was entirely abolished. This principle, however, does appear in the reliefs of the Ara Pacis, and therefore they mark a new era in art. The perspective and the foreshortening are stronger and more illusional. In the background we get flat heads just incised in the marble to give the effect of the depth of the crowd. The scene is in fact not a procession in Indian file but a true crowd many ranks deep. The principle is not altogether adequately carried out in the Ara Pacis, but soon it is more completely mastered. The stucco decorations of the Villa Farnesina,[126] though in the lowest possible relief, express a depth greater than any Hellenistic landscape relief. They are purely pictorial in character. The subordination of sculpture to pictorial ideas is Italian not Greek. Italy through Etruria, her real artistic pioneer, was always a patron of painting rather than sculpture, and therefore under the Empire sculpture becomes either wholly decorative or merely devoted to portraiture. During the reign of Augustus Greek influence still persists, and under Hadrian we have a Greek revival, but from Tiberius to the Renaissance sculpture descends from a primary to a secondary art.