Model of dome and drum

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The model displays the eight sides of the dome, connected by as many angle ribs. Each side presents two vertical ribs and nine transverse arches. Through the cross-section of one of the eight shells of the model, one can observe the openings made in the vertical ribs to obtain four levels of walkways linked by stairs leading from the tambour to the lantern base. The eight angle marble ribs visible from the outside are purely decorative and provide no structural support.

The model also shows that while the inner shell (intrados) has an even thickness, the outer shell (extrados) becomes gradually thinner from the base to the oculus.

Another feature illustrated in the model is the layering of the masonry in one of the eight sides of the dome. One can observe the steep inward slope of the brickwork courses, as well as the slack-line curved profile (a corda blanda) of the horizontal rows of bricks between the angle ribs. The model also highlights the function of the spiral herring-bone arrangement of the bricks, which made it possible to "block" the masonry courses as they were built. The bricks were thus prevented from slipping away as a consequence of the steep inward slope of the masonry beds.

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