Rules · Walls · Materials · Ornament · Vaults
Plaster the walls in several coats and paint them: a dark dado below, the middle zone in panels of red, black or yellow divided by painted bands and architecture, a light zone above; lay the floors with mosaic over a bedding of concrete; vault the best rooms; and keep the cornices of rooms used by firelight and lamplight slender and plain, since smoke spoils fine work.
Vitruvius describes the ancients’ painting of walls as beginning with imitations of marble veneers, then of cornices and architecture, then of views and figures within the panels, and he complains of the fantastic painting of his own day. The houses of Pompeii and Herculaneum, buried in AD 79, show the scheme he describes: a dado, a main zone of panels and a light upper zone.
In the Greek house the walls were plastered and painted in bands, often in imitation of masonry, and the men’s dining room (andron) had a floor of pebble mosaic with a raised border for the couches, as at Olynthus.
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)
An arch cannot support itself until it is complete. Build it on a timber centring shaped to the intrados, strike the centring only when the keystone is set and the mortar has taken, and reuse it from bay to bay, which is one reason to keep the spans of an arcade equal.
In a row of arches the thrusts of neighbouring arches cancel over each intermediate pier, which may therefore be slender; at the ends of the row nothing balances them, so the outermost piers must be made wider or buttressed.
Over a doorway or window spanned by a lintel, turn an arch in the wall above so that the weight of the masonry is carried round the opening onto the jambs, leaving the lintel to carry only the small triangle of wall beneath the arch.
Cite this page Chris Paton, “Roman walls, floors and vaults”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/vitruvius-wall-painting. Text, drawings and models licensed under CC BY-NC 4.0.