Three of them still serve for their ancient use. They are--(1.) The _Acqua Vergine_, the ancient _Aqua Virgo_. (2.) The _Acqua Felice_, named after the conventual name of its restorer Sixtus V. (Fra Felice), is, probably, a part of the ancient _Aqua Claudia_, though some take it for the _Alexandrina_. (3.) The _Acqua Paola_, the ancient _Alsietina_.--The following woodcut represents a restored section of the triple aqueduct of Agrippa:--_a._ the _Aqua Marcia_; _b._ the _Aqua Tepula_; _c._ the _Aqua Julia_. The two latter are of brick and vaulted over. The air-vents are also shown.--The channel of an aqueduct (_specus_, _canalis_) was a trough of brick or stone, lined with cement, and covered with a coping, which was almost always arched; and the water either ran directly through this trough, or it was carried through pipes laid along the trough. These pipes were of lead, or terra-cotta (_fictiles_), and sometimes, for the sake of economy, of leather. At convenient points on the course of the aqueduct, and especially near the middle and end, there was generally a reservoir (_piscina_, _piscina limosa_) in which the water might deposit any sediment that it contained. The water was received, when it reached the walls of the city, in a vast reservoir called _castellum_, which formed the _head of water_ and also served the purpose of a _meter_. From this principal _castellum_ the water flowed into other _castella_, whence it was distributed for public and private use. The term _castellum_ is sometimes also applied to the intermediate reservoirs already mentioned. During the republic, the censors and aediles had the superintendence of the aqueducts. Augustus first established _curatores_ (or _praefecti_) _aquarum_, who were invested with considerable authority. They were attended outside the city by two lictors, three public slaves, a secretary, and other attendants. In the time of Nerva and Trajan, 460 slaves were constantly employed under the orders of the _curatores aquarum_ in attending to the aqueducts. They consisted of:--1. The _villici_, whose duty it was to attend to the pipes and _calices_. 2. The _castellarii_, who had the superintendence of all the _castella_, both within and without the city. 3. The _circuitores_, so called because they had to go from post to post, to examine into the state of the works, and also to keep watch over the labourers employed upon them. 4. The _silicarii_, or paviours. 5. The _tectores_, or masons. These and other workmen appear to have been included under the general term of AQUARII. ĂQUAE ET IGNIS INTERDICTĬO. [EXSILIUM.] ĂQUĀRĬI, slaves who carried water for bathing, &c., into the female apartments. The aquarii were also public officers who attended to the aqueducts. [AQUAE DUCTUS.] ĂQUĬLA. [SIGNA MILITARIA.] [Illustration: Arae, Altars.]