In treating of the Aqueducts we have a trustworthy guide in a writer who flourished in the time of the Emperors Nerva and Trajan, namely, SEXTUS JULIUS FRONTINUS[2]. While he informs us of what improvements he made during the time he had the charge of these important public works, he also gives in his treatise a historical account of the several changes which had been from time to time made in the means of supply of water to the Imperial City, which kept pace with the growing wealth and population of Rome. When he died they had probably reached perfection, and were justly the admiration and surprise of all travellers[3]. His treatise is well worth examination, not only from an archæological point of view, but as suggesting also many curious enquiries as to the engineering abilities which the Romans possessed, compared with those exhibited at the present day. In elucidating, however, the architectural antiquities of the city of Rome, it will be necessary, as far as possible, to limit the extracts from his treatise _De Aquæductibus_, to those portions which refer either directly to existing remains, or which indirectly explain them, by pointing out the principle on which the several Roman aqueducts seem to have succeeded each other. Frontinus tells us in his fourth chapter, that for 441 years after the building of the city, or until B.C. 312, the people were content with the water which they could draw from the Tiber, or from wells[4] or from springs, of some of which the memory was in his time still held sacred and honoured, for they were thought to afford health to the sick[5]. Passing to his own time, he says, “there now flow into the city:”— I. Aqua Appia. II. Anio Vetus. III. Aqua Marcia. IV. ” Tepula. V. ” Julia. VI. Aqua Virgo. VII. ” Alsietina (which is also called Augusta[6]). VIII. ” Claudia. IX. Anio Novus. Frontinus describes the above nine aqueducts in order, giving details as to the source of the water in each, the quantity, and the distribution. Such extracts as are calculated to throw light upon the existing remains, are given in the course of the following remarks. Seven other Aqueducts were added after the time of Frontinus at different periods, of which an account will also be found in the second part of this Chapter. I. THE AQUA APPIA (A.U.C. 441, B.C. 312). “The _Aqua Appia_ was brought into Rome by the censor Appius Claudius Crassus, afterwards called _Cæcus_ (the blind), who also caused the Via Appia to be constructed from the Porta Capena to the city of Capua[7].”