FOUNDATION, in architecture, is that part of a building which is under ground. See BUILDING.
The foundation is properly so much of the masonry as reaches as high as the surface of the ground, and ought always to be proportioned to the load or weight of the building that it is to bear. Sometimes the foundation is massive, and continued under the whole building, as in the antique arches and aqueducts, and some amphitheatres; but it is more usually in spaces or intervals, either to avoid expence, or because the vacancies are at too great a distance, in which latter case they make use of insulated pillars bound together by arches.
Palladio allows a sixth part of the height of the whole building for the hollowing or under-digging; unless there be cellars under ground, in which case he would have it somewhat lower; and as to thickness, double the width of the wall is no bad rule.