The 17 meters wide vault is supported by particularly strong pilasters planned by Alberti in an ingenuous system, which he managed by combining his knowledge of construction techniques with his inventions. All connections are regulated by a modular geometric system, where each space is a multiple of the other, following a principle of rationality and perfection.The powerful pilasters are certainly a novel aspect, from where Alberti obtained the closed chapels, which are covered by small domes and lightened by windows located on the external walls. In the space between the fluted and unfluted pilasters the architect inserted imposing barrel arches, creating the open chapels, which alternate with the closed ones in a continuous rhythm (A-B-A-B) up to where it crosses the transept.The illumination system adds to the dynamism of the space, creating contrast and defining each area: the closed chapels get the light from the side windows while the main body of the church remains in dim light, illuminated only by the oculi above. A full lighting, coming from the dome above, defines the cross between the transept and the main body, putting the presbytery in evidence, and at the same time surrounding it with the dim light of the apse.Everything in the interior has been devised to bring up an inner concentration and a serene and rational contemplation of the divine.