‹‹‹ Vitr. 6.8.3 | Table of Contents | Vitr. 6.8.5 ›››
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.
4Likewise in houses where piers are used in the construction, when there are arches composed of voussoirs with joints radiating to the centre, the outermost piers at these points must be made broader than the others, so that they may have the strength to resist when the wedges, under the pressure of the load of the walls, begin to press along their joints towards the centre, and thus to thrust out the abutments. Hence, if the piers at the ends are of large dimensions, they will hold the voussoirs together, and make such works durable.