It will be well, before beginning this paper, to title. The word architecture is so broadly and so used that one may hardly venture to employ it determined the limit of its application. It is impossible eliminate from architecture the factor of usefulness, this is larger in some structures than in others. predominates, and then people are disposed to call ing. But architecture is distinctively the art of design composition, and the term may be applied to structures though they may have no claim to beauty of detail, evidence, in the composition and proportions of their that their builders had a care for appearances, and aimed at producing an effect of dignity and elegance to the character of the monument. It is in this sense that we shall consider it.
The aqueducts of Rome have been amply and exhaustively treated by writers in ancient and modern times. They have been the subject of the most careful study of civil and hydraulic engineers ever since these two sciences were first developed. Books and papers have been written upon them from the point of view of the engineer and of the archaeologist, from Frontinus, the Curator Aquarum of the Emperor Trajan, to the famous archaeologists of our day. Architectural writers have either omitted all reference to them or have mentioned them only to say that they do not properly belong to the architectural domain. But wherever stone is dressed and laid in regular or symmetrical courses, the elements of architectural evidence; any building in which string courses which the openings are symmetrically disposed, theory of composition and is consequently to architecture; and where mouldings and decorative employed in connection with symmetrical meets the requirements of even the most superficial of the art.
The earliest of the Roman aqueducts that were constructed above ground, could boast of many, if not all, of these elements; the first of them, belonging to the republican era, was not only built of the most carefully cut and fitted blocks of stone, but consisted of a series of piers and arches, designed with the utmost regard to symmetry and proportion, was relieved by projecting string courses, where these were required to break the monotony of the surface and to give finish and character to the design, and was embellished at intervals with carved mouldings. Later, under the Empire, we find patterns wrought in stones of different colors to adorn the arches and the side of the water conduit, and mouldings made by allowing courses of brick to project and cutting them into a desired form. In short, the architecture of the best Roman period can be well studied from an examination of the aqueducts alone. Here we may study the dry, cut stonework which characterized the republican period; the concrete, faced with stone or brick, of the Empire; or design as illustrated in the proportions of mass and space, and in the enrichment of buildings by means of the studied dis- position of materials.
The Roman architects when they built for pleasure drew upon Greek art to furnish decorative details, and concealed the true nature of their construction by a sham of entablatures and col- umns. When they built for utility they were no longer bound to employ imported ornament and depended upon their native sense of symmetry and proportion and upon the use of simple mouldings or of color to secure a sufficiently pleasing effect.The aqueducts are thus perhaps the most truly national struc- tures erected by the Romans, simple, truthfully structural, without the pretence of columns or ornamental entablatures. In this paper, therefore, we shall avoid those portions of the aqueducts that partake of a festal or monumental nature, such as the Porta Maggiore, the Porta San Lorenzo, and the Arch of Dolabella, for these depend upon the ordinary architectural details for their effect, and shall confine our study to the aqueduct itself.
The aqueducts of the Romans may be divided into three general groups, according to the materials of which they are constructed. This classification is the more convenient in that it conforms very nearly to their chronological arrangement. The earliest of these monuments that show any architectural character was built entirely of cut stone, laid dry in regular courses; it belongs to republican times, having been begun 144 B.C. and finished very soon thereafter. During the early Empire the Romans continued to employ tufa and peperino cut and laid in a similar manner, though with rather less care and precision. The greatest of all the Roman aqueducts was so constructed under the Emperor Claudius. But even under Augustus it had become the custom to build the smaller aqueducts, and those in the provinces, of concrete faced with a revetment of stone laid in courses or in the form of opus reticulatum. Some of the most beautiful speci- mens of aqueduct architecture were thus constructed.
But this custom did not obtain for any great length of time. Under Nero the first and finest of the brick-faced aqueducts was built. This period is well known as the best for brickwork. From this time aqueducts, in Italy at least, seem to have been made invariably with brick facing, and all the repairs upon the older aqueducts were carried out in brick, down to the reign of Alex- ander Severus, under whom the last of the great aqueducts was erected. It will thus be seen that the periods of classification overlap slightly, whether we make the division purely chlronological, or according as the aqueducts were constructed of free stone, of concrete faced with or of concrete and brick. It is impossible in a paper of this character to take up all the aqueducts built in the Roman domain. We shall therefore select only the most characteristic examples, wherever found, to illustrate the three classes of aqueducts mentioned.