Before leaving St. Peter’s a word may be said of a project for the building which was prepared by Antonio San Gallo the younger, Michael Angelo’s immediate predecessor as architect for the fabric. This design, no part of which was ever carried out, is embodied in a wooden model preserved with that of Michael Angelo in the existing edifice. The most meritorious feature of this model is the dome which, from a structural point of view, is better than the one that was built, since it is well abutted both at the springing and at the haunch. This important condition is secured, however, by an architectural treatment that cannot be commended, and consists of two superimposed concentric arcades, the lower one surrounding the drum and abutting the vault at the springing, while the upper one is set in retreat and fortifies the haunch. The architectural effect of these arcades, which are of course adorned with classic orders, is not happy because an arcade with a classic order is not an appropriate form of abutment, though it may be made mechanically effective, and also because the upper circle, rising from within the circumference of the lower one, gives the composition an unpleasantly telescopic effect. Our consideration of St. Peter’s has led us to an advanced phase of the church architecture of the Roman Renaissance, and we must now go back and examine a few of the earlier structures in Rome and elsewhere that were produced under the distinctly Roman influence. [Illustration: FIG. 33.]