The refinements of the Parthenon
Curved stylobate, columns leaning inward, thicker and closer-set corner columns and entasis, measured by Penrose and exaggerated here so they can be seen.
The rules it illustrates
The stylobate rises in the middle. Do not lay the stylobate dead level: raise it gently toward the middle of each side, for a perfectly flat platform looks to the eye as if it sagged.
Corner columns a fiftieth thicker. Make the corner columns thicker than the rest by a fiftieth of their diameter, because, seen against the open sky, they look thinner than they are.
Columns lean toward the cella. Set the outer columns so that they incline slightly inward, toward the cella wall, the middle columns of the fronts plumb on their own axes and the corner columns leaning both ways.
The Greek entasis: a barely perceptible swelling. Give the shaft a continuous convex curve from base to necking, departing from a straight taper by only a few hundredths of a diameter, so that the column seems to flex under its load rather than to pinch.
The Parthenon’s ratio of 4 : 9. Let one simple ratio govern the whole: at the Parthenon the lower diameter is to the axial spacing, the width of the stylobate to its length, and the height of the order to the width of the front, all very nearly as 4 is to 9.
Where it appears in the book
In the styles Ancient Greek.
In the chapters The Doric Order, The Classical World.