He also connected their pedestals with the spring of the vault by a series of inverted curves sweeping upwards along the height of the shallow attic.

The omission of these details not only weakened the support given to the arches of the dome, but it also lent a stilted effect to the cupola by abruptly separating the perpendicular lines of the drum and attic from the segment of the vaulting.

This is an error which could even now be repaired, if any enterprising Pope undertook to complete the plan of the model.

It may, indeed, be questioned whether the omission was not due to the difficulty of getting so many colossal statues adequately finished at a period when the fabric still remained imperfect in more essential parts.
Vasari, who lived in close intimacy with Michelangelo, and undoubtedly was familiar with the model, gives a confused but very minute description of the building.

It is clear from this that the dome was designed with two shells, both of which were to be made of carefully selected bricks, the space between them being applied to the purpose of an interior staircase.