Even a plain rectangular wall manifests the interplay of these forces. The horizontal dimension represents the downward and outward force of the weight; the vertical dimension, the upward forces, which prevent the wall from collapsing in itself and hold it upright; while the lateral boundaries give evidence of the inward tension that keeps the mass together. But the most beautiful expressions of architectural forces are to be found in the historical styles. In each style there is a characteristic relationship between the forces, imparting a distinctive feeling. I shall offer a brief analysis of some of these. Many have recognized that the classical Greek construction, as illustrated in the Doric temple, expresses a fine equilibrium between the upward and the downward forces, embodied in the vertical and horizontal lines respectively. The upward force is manifest primarily in the vertical columns, and is emphasized there by the flutings, the slight progressive narrowing toward the top, and the inward effort of the necking just below the echinus. The downward force is embodied in the horizontal lines of the lintel, architrave, cornice, and in the hanging mutules and gutta. The two forces come to rest in the abaci, which, as the crowning members of the columns, directly carry the weight of the entire entablature. The equilibrium between the horizontal and the vertical tendencies is, however, not a static but a moving one; for the two opposing forces are present in every part of the building from the stylobate to the ridge of the triangular pediment. The downward force is already manifest in the widened base of the column, where it works in conjunction with the inward tendency, and shows its effect at the critical points at the top of the supporting column--in the spreading echinus with its horizontal bands beneath and in the horizontal lines of the abaci. The upward force, on the other hand, is continued right through the solid mass of the entablature, in the vertical lines of the triglyphs, in the antefixes, and even to the very apex of the building, where the ascending lines of the triangular pediment meet. The resulting total effect is that of a perfect, yet swaying balance.