In his survey of desirable floor plans for sacred buildings – "temples" in his phrase—Alberti begins with the ideal form of the circle, which is expressed in numerous examples of Nature. Nine ideal centrally– planned geometrical shapes are recommended for churches; besides the circle he lists the square, the hexagon, octagon, decagon, and dodecagon, all derived from the circle, and, derived from the square, rectangles that exhibit the square and a half, square and a third and double square, all of which have enharmonic parallels in music. Chapels add small geometric figures to the basic circles and polygons to give a great variety of floor plans, in which each geometrical figure retains its clear unity and simple ratios that bind all elements of the plans and elevations into a harmonic unity.
