The combination of the stability with such lightness and gracefulness as were procurable, can in a measure be estimated by the comparative area taken up by the walls, pillars, and other points of support. This area amounts to seventeen per cent., and compares favourably with St. Peter's at Rome, which is more than half as much again, as well as with St. Sophia and the Duomo at Florence. On the other hand many of our Gothic cathedrals require only ten per cent.[70] Wren would have said that they lack stability, and that he had calculated accurately on the minimum of massiveness requisite for security; and besides this, they have no heavy dome to be poised. Throughout there are two stages or stories. The lower has the Corinthian Order, which was always Wren's favourite, as he held that it was at once more graceful and bore a greater weight of entablature than the earlier Doric and Ionic. Wren's first design of a Greek Cross followed St. Peter's in consisting of one main order plus an attic.[71] While Bramante at St. Peter's found stones of nine feet in diameter in the quarries of Tivoli, Wren, after making inquiries all over, could not procure sufficient stone for his columns and pilasters of a greater diameter than four feet, and he would not depart, at least to any degree, from what he held to be the correct Corinthian height of nine diameters. Had a sufficient quantity of larger blocks been obtainable, we should have had the Corinthian order plus the attic, instead of the two regular orders of Corinthian and Composite.[72] And this, it seems, was his reason for departing in this respect from the First Design; as also partially from the Approved Design. The pilasters are grouped in pairs throughout, not only for stability, but also for sufficient space for the circular-headed windows ornamented with festoons. Above the entablature rises the second stage or story, or order. Here the coupled pilasters have that slight difference in base and more particularly in capital which constitutes the Composite order. The capitals have the larger scrolls or volutes of the Ionic above the acanthus leaves of the Corinthian proper. In reality the difference is, here, but slight; and the best authorities maintain that there is less difference between the Corinthian and the Composite than between different examples of the Corinthian itself. The reason for the dressed niches, with pediments instead of windows, like those in the lower stage, will come later on. A main architrave and cornice run round the entire building like an unbroken string course, and above this, excepting at the different fronts, a balustrade, to which a history is attached.