Over the first great cornice within the tribune there begin at the foot the compartments for the recesses that are in the vault of the tribune, which are formed by sixteen projecting ribs. These at the foot are as broad as the breadth of the two pilasters which at the lower end border each window below the vault of the tribune, and they rise, diminishing pyramidally, as far as the eye of the lantern; at the foot they rest on pedestals of the same breadth and twelve palms high, and these pedestals rest on the level platform of the cornice which goes in a circle right round the tribune. Above this, in the recessed spaces between the ribs, there are eight large ovals, each twenty-nine palms high, and over them a number of straight-sided compartments that are wider at the foot and narrower at the top, and twenty-four palms high, and then, the ribs drawing together, there comes above each straight-sided compartment a round fourteen palms high; so that there come to be eight ovals, eight straight-sided compartments, and eight rounds, each range forming recesses that grow more shallow in succession. The ground of all these displays extraordinary richness, for Michelagnolo intended to make the ribs and the ornaments of the said ovals, straight-sided compartments, and rounds, all corniced in travertine. It remains for us to make mention of the surface and adornment of the arch on that side of the vault where the roofing is to go, which begins to rise from a base twenty-five palms and a half high, which has at the foot a basement that has a projection of two palms, as have the crowning mouldings at the top. The covering or roofing with which he proposed to cover it is of lead, such as covers the roof of the old S. Pietro at the present day, and is divided into sixteen sections from one solid base to another, each base beginning where the two columns end, which are one on either side of it. In each of these sections, in the centre, he made two windows to give light to the inner space where the ascent of the stairs is, between the two shells, so that in all they are thirty-two. These, by means of brackets that support a quarter-round, he made projecting from the roof in such a manner as to protect the lofty and novel view-point from the rain. In a line with the centre of the solid base between each two columns, above which was the crowning cornice, sprang a rib, one to each, wider at the foot and narrowing at the top; in all sixteen ribs, five palms broad, in the centre of each of which was a quadrangular channel one palm and a half wide, within which is formed an ascent of steps about one palm high, by which to ascend or descend between the platform at the foot and the summit where the lantern begins. These are to be built of travertine and constructed with mortisings, to the end that the joins may be protected against water and ice during times of rain.