This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol5", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
In order to give that stability and spread to the walls at the base of a structure which is necessary to provide a solid foundation, and at the same time to economise both in weight of superstructure and material, recourse is had to simple bands or a series of such termed Bases or " Plinths." These devices act as a means of leading the eye from a too abrupt transition from the solid mass of wall arising out of the ground to the lighter upper parts, and when treated on an artistic basis tend to soften the abrupt change caused by the diminution of the wall face.
In Classical examples, plinths are usually composed of a base course finished with more or less elaborate mouldings, as in Fig. 137, these being usually either parts of conic sections or of circles, as their characteristics more nearly approach the Grecian or Roman types.
It will naturally occur to the professional mind that the fundamental principles in designing base mouldings would be - 1st, the protection of the joints from wet by keeping them in the recesses of the mouldings as far as possible; 2nd, not to arrange any of the members in such a manner as to present cavities or hollows for wet to lie in.
These two points being duly considered, there yet lies a large field for artistic variety in the arrangement of the members, either in Classic, but more particularly in Gothic structures (see Chapter XV (General Details Of Masonry - Gothic).).
Above the base a band of ashlar, of varying height proportionate to the superstructure, is often applied.