The first set of plans of Santo Spirito were drawn up in 1428. Brunelleschi immediately understood the idea to modify the positioning of the church so that it would face onto a piazza, which would in turn face the Arno. According to Brunelleschi, the relationship between architecture and the city was of utmost importance. However, several families on the commission that was supposed to approve the project did not agree with him. These families possessed homes and storage spaces in the area that spanned from the Arno to the church. The largest room is the Old Sacristy, and it is the same size as the Pazzi Chapel. The width of both San Lorenzo and Santo Spirito is almost the same. This confirms that for Brunelleschi, structures had to be constructed as if they were summary modules of the space—independent of the position or size of the building in question. However, in Santo Spirito, the central nave is exactly double the size of the lateral naves, and in San Lorenzo they are closer. In Santo Spirito, Brunelleschi tried to solve the complexity of the building by repeating elements that were the same, and presenting them as referents of a singular building. By controlling proportions and size, Brunelleschi wanted to turn this concept into practice: the multiplication of unity. As for the articulation of space, while in San Lorenzo there were columns and pilasters of differing heights, in Santo Spirito the columns are all the same height. In every plan, every rectilinear wall was eliminated and the concavity and convexity of the perimeter chapels expressed continuity. Thus, the relationship between the internal and the external helped Brunelleschi achieve his idea of circularity.
Source APT di Firenze