The oval church
An oval plan under an oval coffered dome, as in Bernini’s Sant’Andrea al Quirinale (transverse) or Borromini’s San Carlo (longitudinal), with a temple front or an undulating façade.
The rules it illustrates
The giant order. To unify a façade of two or more storeys, run a single order of pilasters or columns through all of them, from the base to the main cornice.
The oval plan. To combine the unity of a central plan with the direction a church needs, plan the space as an oval, set across the axis to widen the view of the altar, or along it to lead the eye towards it.
Coffers that diminish towards the lantern. Divide the inside of a dome into coffers that shrink in step with the meridians as they rise, so that their perspective deepens the dome and draws the eye to the light of the lantern.
The undulating front. Let the wall of a façade curve in plan (concave, convex, concave) so that the front answers the street, the light and the space within, and the order bends with it.
Light from a hidden source. Light the climax of a Baroque interior (the altar or the dome) from windows the visitor cannot see, so that it seems to glow of itself.
The ellipse belongs inside. Use the elliptical plan chiefly for interiors, where the whole curve is seen at once; on the outside of any but a very large building its changing curvature looks like a distorted circle, and the circle is better.
Where it appears in the book
In the styles Baroque, Rococo.
In the chapters Renaissance and Baroque.