Rules · Walls · Entablatures · Structure
Where the architrave runs on over the end of a wall, widen the wall’s end into an anta at least as broad as the architrave, so that the beam has a full bearing and the wall looks able to take it, even if the wall itself is thinner.
Mauch shows the principle at the Propylaea of Eleusis, whose walls carry the same entablature as the columns but are thinner than the architrave. The anta is thickened to the architrave’s width, inside as well as out, and made broader still where a beam ties it to a column opposite.
He also shows its misuse: at the little temple of Diana at Eleusis the anta is so heavy that it sits badly with the corner triglyph, whereas at the Erechtheum a very broad anta is handled so that it stays in scale.
A beam is squeezed along its top and stretched along its bottom; stone resists squeezing well but stretching badly, so a stone lintel must be deep in proportion to its span and cannot be long. Doubling the span quadruples the stress from its own weight.
σ ≈ ¾ ρ g L² ⁄ d (self-weight) · + ≈ 0.43 ρ g L³ ⁄ d² (a wall above)
In a bonded masonry wall the courses above an opening corbel over it of their own accord, so the lintel carries roughly the triangle of wall with sides rising at 60° from its ends; everything above that triangle arches onto the jambs.
load ≈ equilateral triangle on the span: W ≈ 0.43 · L² · t · ρ g
Weight for weight, timber is many times stronger in bending than stone; long spans in trabeated buildings are therefore roofed with timber beams resting on stone walls and columns.
bending strength ÷ density: oak ≈ 70 · limestone ≈ 3 (kPa per kg ⁄ m³)
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)
To end the frieze with a triglyph at the corner and keep every metope square, move the corner column inward: make the last intercolumniation narrower than the others by the amount the corner triglyph is displaced.
contraction c = e − t⁄2; Parthenon: 4.29 m normal, 3.68 m at the corners (c ≈ 0.61 m)
Cite this page Chris Paton, “An anta as wide as the architrave it carries”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/mauch-anta-width. Text, drawings and models licensed under CC BY-NC 4.0.