We may recognize this union, as it actually arises, clearly in the transformation now introduced of that which we already have met with in the architecture which was anterior under the form of columns. In other words, it is true that from one point of view walls are necessary to make an enclosure; but walls, too, can stand up independent, as we have already proved with examples, without making the enclosure complete, to which a roofing, no less than an enclosure of the sides, essentially contributes. But a roofing of this kind has to be supported. The simplest way of doing this is by columns, whose essential and, at the same time exclusive, rationale consists here in being simply _supports._ For this reason walls are really a superfluity is so far as it is only a question of support. For supporting is a mechanical relation, and belongs to a province of gravity and its laws. And in this[71] gravity the weight of a particular body is concentrated in its point of gravity, and must be assisted at this centre in remaining horizontal without a fall. This is precisely what the column does, so that with it the power of support appears to be reduced to the minimum limit of exterior means to effect this. What a wall at great cost[72] effects, is equally effected by a few columns. It is a very beautiful characteristic of classic architecture not to set up more columns than are actually necessary to carry the weight of the rafter and that which reposes thereon. In genuine architecture columns, for purposes of mere decoration, are not truly beautiful. For the same reason also columns which stand up entirely alone do not perform their true function. No doubt triumphal columns have been erected, such as the famous ones in honour of Trajan and Napoleon: but these, too, are really but a pedestal for statues, and moreover covered with sculptured reliefs to commemorate and glorify the hero, whose image they carry. In the case of the column, then, it is of exceptional importance to see how in the course of architectural development it is compelled to divest itself of the concrete form of Nature before it can secure its more abstract form, the form, that is, which is as compatible with a definite object as it is with beauty.