Ad Quadratum
On page 204, the author repeats his claim that "according to the system of Cesario applied to Milan Cathedral the rhombus formed the basis upon which the plan for the church was constructed". Clearly he is speaking of the elevation and not the floor plan, because, as you can see, the floor is a grid of squares. Note that the circle that I have drawn at the center of the crossing of the nave and transcepts contains both a square and an octogon.