AQUEDUCTS.--The aqueducts of ancient Rome were among the most important of the utilitarian works of the Romans. The water-system of the capital was commenced by Appius Claudius (about 313 B.C.), who secured the building of an aqueduct which led water into the city from the Sabine hills. During the republic four aqueducts in all were completed; under the emperors the number was increased to fourteen. [Footnote: Several of these are still in use.] The longest of these was about fifty-five miles in length. The aqueducts usually ran beneath the surface, but when a depression was to be crossed, they were lifted on arches, which sometimes were over one hundred feet high. These lofty arches running in long broken lines over the plains beyond the walls of Rome, are the most striking feature of the Campagna at the present time. THERMÆ, OR BATHS.--The greatest demand upon the streams of water poured into Rome by the aqueducts was made by the Thermæ, or baths. Among the ancients Romans, bathing, regarded at first simply as a troublesome necessity, became in time a luxurious art. Under the republic, bathing- houses were erected in considerable numbers. But it was during the imperial period that those magnificent structures to which the name of Thermæ properly attaches, were erected. These edifices were among the most elaborate and expensive of the imperial works. They contained chambers for cold, hot, tepid, sudatory, and swimming baths; dressing-rooms and gymnasia; museums and libraries; covered colonnades for lounging and conversation, extensive grounds filled with statues and traversed by pleasant walks; and every other adjunct that could add to the sense of luxury and relaxation. Being intended to exhibit the liberality of their builders, they were thrown open to the public free of charge. MEMORIAL ARCHITECTURE.--Among the memorial structures of the Romans, their triumphal arches are especially characteristic. These were modelled after the city gates, being constructed with single and with triple archways. Two of the most noted monuments of this character, and the most interesting because of their historic connections, are the Arch of Titus (see p. 315) and the Arch of Constantine, both of which are still standing. The Arch of Constantine was intended to commemorate the victory of that emperor over his rival Maxentius, which event established Christianity as the imperial and favored religion of the empire. [Illustration: ARCH OF CONSTANTINE.] 2. LITERATURE, PHILOSOPHY, AND LAW. RELATION OF ROMAN TO GREEK LITERATURE: THE POETS OF THE REPUBLICAN ERA.-- Latin literature was almost wholly imitative or borrowed, being a reproduction of Greek models; still it performed a most important service for civilization: it was the medium for the dissemination throughout the world of the rich literary treasures of Greece.