Now, coming back to the axiom before mentioned, that architectural design should express and emphasize the practical requirements and physical conditions of the building, let us look a little more in detail into the manner in which this may be done. We will take, to begin with, the very simplest structure we can possibly build--a plain wall (Fig. 1).[2] Here there is no expression at all; only stones piled one on another, with sufficient care in coursing and jointing to give stability to the structure. It is better for the wall, constructively, however, that it should have a wider base, to give it more solidity of foundation, and that the coping should project beyond the face of the wall, in order to throw the rain off, and these two requirements may be treated so as to give architectural expression to our work (Fig. 2). It now consists of three distinct portions--a plinth, or base, a superficies of wall, and a coping. We will mark the thickening at the base by a moulding, which will give a few horizontal lines (at B), and the coping in the same way. The moulding of the coping must also be so designed as to have a hollow throating, which will act as a drip, to keep the rain from running round the under side of the coping and down the wall. We may then break up the superficies by inserting a band of single ornament in one course of this portion of the wall--not half way, for to divide any portion of a building into mere "halves" has usually a weak and monotonous effect, but about two thirds of the distance from the base line; and this band of ornament not only breaks up the plain surface a little, but also, by carrying another horizontal line along the wall, emphasizes its horizontality. Always emphasize that which is the essential characteristic of your structure. A wall of this kind is essentially a long horizontal boundary. Emphasize its length and horizontality. [Footnote 2: The dark shaded portion in this and the next two diagrams show the "section" of the wall as seen if we cut it through and look at it endwise.] If we are millionaires, and can afford to spend a great deal on a wall, we may not only (Fig. 3) carry further the treatment of the coping and base, by giving them ornamental adjuncts as well as mouldings, but we might treat the whole wall superficies as a space for surface carving, not mechanically repeated, but with continual variation of every portion, so as to render our wall a matter of interest and beauty while retaining all its usefulness as a boundary, observing that such surface ornament should be designed so as to fulfill a double object: 1, to give general relief to the surface of the wall; 2, to afford matter of interest to the eye on close inspection and in detail.