In Bramante’s project every essential feature of this ancient monument is reproduced, but with modifications which give a different aspect to the design as a whole, but do not constitute any such radical departure from the principles embodied in the Pantheon as those wrought by Brunelleschi in adapting the scheme of the Baptistery to that of the dome of the cathedral of Florence. In order to secure greater elevation for external effect, the architect has raised the springing level of the dome considerably, though he has still kept it below the top of the drum. The drum itself is of great thickness, and forms a strong continuous abutment at the springing, and the haunch of the vault is loaded with steps of masonry as in the Pantheon, though not quite so heavily. The lower half of the drum is a solid wall resting on the pendentives, while the upper part, which is less than half as thick (Fig. 25), is pierced with eight wide openings, and its inner and outer faces are each adorned with an order of pilasters alternating with free-standing columns in the intervals. The upper wall stands on the inner circumference of the massive lower ring, while an encircling order of Corinthian columns is ranged on its outer circumference, and gives an effect of lightness and elegance to the exterior, which, together with the lantern at the crown of the dome, goes far to disguise the real likeness of the whole to the Pantheon scheme. [Illustration: FIG. 25.--Plan of Bramante’s dome, from Serlio.] In these changes and additions Bramante was governed by a clear understanding of the exigencies of his project. He was obliged to raise the internal order from the place on the ground level which it occupies in the Pantheon, to the upper part of the drum, in order to provide a solid foundation resting on the pendentives; and this compelled him to eliminate the attic story of the Pantheon scheme. The most radical change was that of substituting the open colonnade for the solid wall on the outside of the drum. It is doubtful, I think, whether the drum thus lightened would have had enough strength to withstand the enormous thrusts of such a dome. Like the dome of the Pantheon, Bramante’s dome was to be hemispherical and to have an opening at its crown. Over this he was to set the lantern which in outline recalls that of Brunelleschi, though it is of lower proportions, in keeping with the less elevated form of his dome, and has a small hemispherical dome instead of a conical roof. The shape of the lantern accords well with the composition as a whole, and contributes much to the aspiring expression which was now demanded, without wholly contradicting the classical spirit that the architect was striving to maintain.