The Ten Books on Architecture, 6.8

Vitruvius  translated by Joseph Gwilt

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Of the Strength of Buildings

8In those buildings which are raised from the level of the ground, if the foundations are laid according to the rules given in the preceding books for the construction of walls and theatres, they will be very durable; but if under-ground apartments (hypogea) and vaults are to be built, their foundations must be thicker than the walls of the upper part of the edifice, which, as well as the pilasters and columns, must stand vertically over the middle of the foundations below, so that they may be on the solid part. For if the weight of the walls or the columns have a false bearing, they cannot last long.

2It is, moreover, a good practice to place posts under the lintels, between the piers and pilasters; for when lintels and beams are loaded, they sag in the middle, and cause fractures in the work above: but when posts are introduced and wedged up under them, the beams are prevented from sagging and being injured.

3Care also should be taken to discharge the weight of walls by arches consisting of wedges concentrically arranged; for if these are turned over beams or lintels, the beam, being relieved from the weight, will not sag; and when afterwards it is decayed through age, it may be easily replaced, without the necessity of shores.

4So in buildings, which are constructed on piers and arches, consisting of wedges whose joints are concentric, the outer piers should be wider than the others, that they may have more power to resist the action of the wedges, which, loaded with the weight of the superincumbent wall, press towards the centre, and have a tendency to thrust out the abutments. But if the outer piers be of large dimensions, by restraining the power of the wedges they will give stability to the work.

5Having paid due attention to these points, care must next be taken, and particularly is it to be observed, that the work be carried up perpendicularly and without inclination in any part. The greatest attention must be bestowed on the lower parts of the walls, which are often damaged by the earth lying against them. This is not always of the same weight as in summer; for in the winter season, imbibing a great quantity of water from the rain, it increases in weight and bulk, and breaks and extrudes the walls.

6To remedy this evil, the thickness of the wall must be proportioned to the weight of earth against it, and, in front, counterforts (anterides) or buttresses (erismæ) are carried up with the wall, at a distance from each other equal to the height of the foundations, and of the same width as the foundations. Their projection at bottom is equal in thickness to the wall, and diminishing as they rise, their projection at top is equal to the thickness of the work:

7adjoining the inside of the wall, towards the mass of ground, teeth similar to those of a saw are constructed, each of which projects from the wall a distance equal to the height of the foundations, and their thickness is to be equal to that of the foundation wall. An extent equal to the height of the foundations is taken at the outer angles, and marked by points on each side; and through these a diagonal is drawn, on which a wall is carried up, and from the middle of this another is attached to the angle of the wall. The teeth and diagonal walls being thus constructed, will discharge the weight of earth from the wall, by distributing its pressure over a large surface.

8Thus I have described the precautions to be taken at the beginning of a building, to prevent defects. The same importance does not attach to the roof, with its beams and rafters, because if these at any time are found defective, they may be easily changed. I have also explained how those parts which are not built solid are to be strengthened.

9The quality of the materials it is not in the power of the architect to control: for the same species of materials are not found in every place; and it depends on the employer whether the building shall be of brick, of rough stone, or of squared stone. The merit of every work is considered under three heads; the excellence of the workmanship, and the magnificence and design thereof. When a work is conducted as magnificently as possible, its cost is admired; when well built, the skill of the workman is praised; when beautifully, the merit belongs to the architect, on account of the proportion and symmetry which enter into the design.

10These will ever be apparent when he submits to listen to the opinions even of workmen, and ignorant persons. For other men, as well as architects, can distinguish the good from the bad; but between the ignorant man and the architect there is this difference, that the first can form no judgment till he sees the thing itself; whereas the architect, having a perfect idea in his mind, can perceive the beauty, convenience, and propriety of his design, before it is begun. I have laid down as clearly as I could the rules necessary for the construction of private buildings: in the following book I shall treat of the method of finishing them, so that they may be elegant and durable.

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