The Chapel of San Castrense has a strongly longitudinal schematic layout, which is also due to the mirrored location of the altar and the founder’s tomb. The roof is divided in a simple and linear way into three equal parts by a system of round arches. The division is also noticeable thanks to the pilasters which become real pillars at certain strategic points where they support the dome, as well as around Cardinal Ludovico II de Torres’ monument. The entire chapel’s barrel vault, however, has the same curvature as the arches and sits on the perimeter frame of the building.