Among the Greeks, open structures, colonnades and porticoes, have as object the promenade in the open air, conversation, public life under a pure sky. Likewise the dwellings of private persons are insignificant. Among the Romans, on the contrary, whose national architecture has a more positive end in utility, appears later the luxury of private houses, palaces, villas, theatres, circuses, amphitheatres, aqueducts and fountains. But the principal edifice is that whose end is most remote from the wants of material life; it is the temple designed to serve as a shelter to a divine object, which already belongs to the fine arts—to the statue of a god. Although devoted to a determinate end, this architecture is none the less free from it, in the sense, that it disengages itself from organic forms; it is more free even than sculpture, which is obliged to reproduce them; it invents its plan, the general configuration, and it displays in external forms all the richness of the imagination; it has no other laws than those of good taste and harmony; it labors without a direct model. Nevertheless, it works within a limited domain, that of mathematical figures, and it is subjected to the laws of mechanics. Here must be preserved, first of all, the relations between the width, the length, the height of the edifice; the exact proportions of the columns according to their thickness, the weight to be supported, the intervals, the number of columns, the style, the simplicity of the ornaments. It is this which gives to the theory of this art, and in particular of this form of architecture, the character of dryness and abstraction. But there dominates throughout, a natural eurythmy, which their perfectly accurate sense enabled the Greeks to find and fix as the measure and rule of the beautiful.