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 · Geometry
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.
Parthenon: greatest departure ≈ 1.7 cm on a shaft 9.6 m high (≈ 1⁄110 D)
Vitruvius mentions entasis and promised a diagram, now lost. The Greek examples measured by Penrose show a curve quite different from the Renaissance method of keeping the lower third cylindrical (see Vignola’s entasis: straight for a third, curved above): the swelling starts at the base and is greatest about two-fifths of the way up, and in the Parthenon it is so slight that it cannot be seen as a curve at all, only felt as a certain vitality in the shaft.
Archaic columns, such as those of the “Basilica” (the first temple of Hera) at Paestum, have a far more pronounced entasis, almost a bulge. The history of the Doric column in the sixth and fifth centuries is in part a history of making the curve subtler.
Related rules
Plan the principal hall as a long rectangle entered on its short side through a porch with two columns between the side walls and a vestibule, and put a great round hearth in the centre of the hall, ringed by four columns carrying a raised roof.
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
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
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
A Doric frieze cannot obey all three of its rules at a corner: triglyphs over the column axes, a triglyph turning the corner, and metopes as broad as they are high. One of them must give way.
displacement of the corner triglyph = e − t⁄2 (e = half-depth of the architrave, t = triglyph width)
Cite this page Chris Paton, “The Greek entasis: a barely perceptible swelling”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/greek-entasis. Text, drawings and models licensed under CC BY-NC 4.0.