Cut a shaft with sixteen shallow flutes or facets, give it a square abacus and a low round base: the “proto-Doric” column of the Middle Kingdom rock tombs at Beni Hasan.
Rules · Columns · Optics · Proportion
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.
D corner = D × (1 + 1⁄50); Parthenon: 1.95 m against 1.905 m
Vitruvius explains that air “eats away” at a column silhouetted against the light, so the corner columns, which have nothing behind them, must be thickened to look equal to their neighbours. The same passage makes the general point that the thickness of a column must grow with the width of the space around it.
Penrose found exactly such a thickening at the Parthenon, where the corner shafts are a little over 2 % stouter than the others, close to Vitruvius’s fiftieth. It is combined with the narrowing of the end bays, so that the corners are visibly firmer, as a frame should be.
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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.
Parthenon: rise ≈ 11 cm over 69.5 m (flanks), ≈ 6.5 cm over 30.9 m (fronts), about 1 : 600
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.
Parthenon: lean ≈ 6–7 cm over 10.43 m (≈ 1 : 150); the axes would meet some 2 km above the ground
Cite this page Chris Paton, “Corner columns a fiftieth thicker”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/corner-column-thickening. Text, drawings and models licensed under CC BY-NC 4.0.