Brunelleschi’s dome
The octagonal double-shell dome of Florence Cathedral: pointed-fifth profile, eight angle ribs and sixteen hidden ribs, drum with oculi, lantern.
The rules it illustrates
The pointed fifth. Draw the curve of a pointed dome with arcs whose radius is four-fifths of the span, their centres standing on the springing line one-fifth of the span in from the opposite side.
Two shells tied by ribs. Build a great dome as two shells (a thick inner one that carries, a thin outer one that protects and gives the silhouette) joined by ribs and locked at the top by a ring under the lantern.
Building a dome without centering. Lay the brickwork of a large dome in horizontal rings, each ring locked by bricks set on end in a herringbone pattern, so that every stage of the work stands by itself without a timber frame beneath it.
Where it appears in the book
In the styles Renaissance.
In the chapters Renaissance and Baroque.