The scheme was clearly based on the model of St. Peter’s in Rome, to which frequent reference is made in _Parentalia_ as having been in the mind of the architect as he developed his idea. The dome partakes of the character of Bramante’s design on the one hand, and of that of Michael Angelo, as finally constructed, on the other. The likeness to Bramante’s scheme (Fig. 23, p. 48) is in the form of the inner shell, and its adjustment to the supporting drum. The likeness as to adjustment is not, indeed, very close; for Wren has raised the springing so that it is almost at the top of the drum, but he has fortified it with a continuous abutment which, though of different outline, has substantially the same structural effect. The likeness to St. Peter’s is further shown in the encircling order of the inner face of the drum, which occurs in both Bramante’s scheme and in that of Michael Angelo. There can be little doubt that Wren had studied Bramante’s design in Serlio’s book, and had appreciated its structural merits. But he wished, in emulation of Michael Angelo, to make his dome externally more imposing, and he therefore raised its springing level as we see, and adopted from Michael Angelo’s scheme the idea of a double dome. The external outline from the top of the drum to the haunch of the vault is too nearly the same as the corresponding part of Michael Angelo’s design to be considered as an accidental coincidence. The structural difference between the two is indeed great, since the concave portion in Wren’s design is a continuous ring, while in that of Michael Angelo it is an isolated and insignificant abutment. Wren’s scheme is thus superior in point of constructive merit, since it provides continuous resistance to continuous thrust. It will be seen that the two shells of Wren’s projected dome correspond to the inner and outer shells of Michael Angelo’s model (Fig. 26, p. 54), and thus in reproducing the main idea of this model Wren merely omitted the middle shell. He thus gave a wider divergence to the two vaults as they rise than occurs in the actual dome of St. Peter’s. He also omitted the well which in St. Peter’s connects the two shells at the crown. A single order of pilasters adorns both the interior and the exterior of the church itself, the one on the outside being raised on a high basement and crowned with a plain attic; and a portico in the form of a temple front, with its order raised on high pedestals, gives emphasis to the west façade.