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AQUAEDUCTUS (ὑδραγωγία, ὑπόνομος)--literally, a water-conduit--would, of course, properly describe any channel for the passage of water; but the word is used especially for the magnificent structures by means of which Rome and other cities of the Roman empire were supplied with water, and which may be described in general terms as channels, constructed as nearly as possible with a regular declivity from the source whence the water was derived to the place where it was delivered, carried through hills by means of tunnels, and over valleys upon a substruction of solid masonry or arches.

1. Greek.

Among the Greeks in many cases. springs (κρῆναι, κρουνοί) were sufficiently abundant to supply a considerable part of the great cities with water; and great attention was paid to the preservation and adornment of them: they were converted into public fountains by the formation of a head for their waters, and the erection of an ornamental superstructure; and were dedicated to some god or hero. Pausanias (10.4.1) considers no place to deserve the name of city which has not such a fountain. We are indebted to the same author and other Greek writers for accounts of some of the most celebrated fountains: such as that of Theagenes, at [p. 1.147]Megara (Paus. 1.40.1); those of Peirene and Lerna at Corinth, where there were many other fountains, as well as a Roman aqueduct erected by Hadrian (2.3, § § 2, 3, 5; 4.5); that in the grove of Aesculapius at Epidaurus (2.17.5); and several others (4.31, 32, 34; 7.5, 21; 8.13), of which we need only mention the Enneakrounos at Athens, which was constructed by Peisistratus and his sons, and of which Thucydides records the interesting fact, marking the transition from the natural springs to the artificial fountain, and showing the importance attached even to the former, that “it was called Callirhoë formerly, when the springs were visible” (φανερῶν τῶν πηγῶν οὐσῶν, Thuc. 2.15; Paus. 1.14.1): to this enumeration might be added the springs of salt water in certain temples; as in those of Erechtheus at Athens, and of Poseidon Hippius at Mantineia. (Paus. 1.26.5; 8.10.4.)

In these cases we have no reason to suppose that there was anything more than a fountain over or close to the springs, forming a head for the water derived, either immediately, or by very short channels, from them. But we are not without examples of constructions more nearly approaching the Roman aqueducts in kind, though not in degree. That the Greeks, at a very early period, had some powers of hydraulic engineering, is shown by the drainage tunnels of the lake Copaïs, and the similar works of Phaeax at Agrigentum [EMISSARIUM]; and we have an instance of a channel for water being carried through a mountain, to supply the city of Samos. The height of the mountain was 150 orguiae (900 Greek feet); the length of the tunnel was 7 stadia (7-8ths of a Roman mile, or about 1420 yards); its section was a square of 8 Greek feet. The actual channel for the water was cut below this, and was, if the text is right, 30 Greek feet deep, and 3 wide; the water passed through pipes (διὰ σωλήνων) from a copious spring, and was thus brought to the city. (Hdt. 3.60.) There are still remains of this tunnel. Müller conjectures that the work was one of those executed by Polycrates (Archäol. d. Kunst, § 81). Indeed many of the Greek waterworks appear to date from the age of the Tyrants.

But from early times, the Greeks, where the needs of a city called for it, constructed underground conduits following the undulations of the surface or carried through the hills by tunnels, and closely resembling the earlier Oriental aqueducts, of which they were probably imitations. Thus the conduit which supplied the acropolis of Thebes was attributed to Cadmus (Dicaearch. p. 143, Fuhr), and the canalisation of the mountain torrents round Argos to Danaus (Strabo, viii. pp. 370, 388). The Greek aqueducts were usually rectangular channels cut in the rock or constructed of solid masonry, but in the Troad we have an instance of one composed of earthenware pipes (Hahn, Ausgrab. auf der Homer. Pergamus).

At Athens the rocky part of the city was dependent on cisterns. Two conduits entered the city on the east from the upper course of the Ilissus, which lower down was canalised, and part of its water went to supplement the Enneakrounos, below which an underground conduit ran from the river, repeatedly crossing under its bed, and accessible to use by shafts, and finally carried to the Peiraeus. Below the Enneakrounos a stream from Hymettus was carried over the Ilissus into the city. Later, two large conduits were constructed from Lycabettus on the east and west of that mountain. A system of canals from the Cephissus served to irrigate the olive-woods. (E. Curtius, VII. Karten von Athen.) Finally, Hadrian, at the end of his reign, built an aqueduct of the Roman type, drawing its water from the Cephissus. Among the finest and best preserved of Greek aqueducts are those of Syracuse, which Thucydides (6.100) tells us were laid under ground to bring drinking-water into the city. They are still in use-one from the Anapus, on the north, twelve miles long, which finally crosses under the Small Harbour and feeds the fountain of Arethusa, and one from the springs of Mount Crimiti on the south. (Schubring, Philologus, 1865, pp. 577-638.)

Solon, according to Plutarch (Plut. Sol. 23), ordained that water might be fetched from the public fountains or wells to a distance of four stadia; beyond this, persons must dig their own wells; but if any one dug to a depth of ten orguiae without finding water, he was permitted to take from his neighbour's well a pitcher of six choës twice a day. Plato (Leg. viii. p. 844, A, B) mentions this law, which obviously refers to country life, in vaguer terms, and also the conditions under which the waters of streams might be diverted for irrigation. The public conduits were superintended by ἐπιστάται τῶν ὑδάτων. Their office was apparently of some importance, as it was held by Themistocles, who inflicted fines on fraudulent consumers (Plut. Themist. 31). The κρηνόφυλακες and κρήναρχοι were probably subordinate officers (Phot. and Hesych. s. vv.; Schömann, Antiq. i. p. 416, E. T.). On Greek aqueducts see E. Curtius, Ueber städtische Wasserbauten der Hellenen, in Archäol. Zeitung, 1847.

2. Roman.

The Romans were in a very different position, with respect to the supply of water, from most of the Greek cities. They at first had recourse to the Tiber and to wells sunk in the city; but the water obtained from those sources was very unwholesome, and must soon have proved insufficient. Consequently, to supply the demands of the public baths and the fullers, and later of the growing population, and later still of the naumachiae, they had recourse to public works in order to bring pure water from a considerable distance--from the hills, in fact, which surround the Campagna. The date of the first aqueduct. is assigned by Frontinus to the year A.U.C. 441, or B.C. 312 (de Aquaed. Urb. Rom. 4); and the number of aqueducts was gradually increased, partly at the public expense and partly by the munificence of individuals, till, in the time of Procopius, they amounted to fourteen (see p. 151 a); and, even before they were all erected, they might well excite the admiration which Pliny expresses with respect to the Claudian aqueduct (H. N. 36.123);--“But if any one will carefully calculate the quantity of the public supply of water, for baths, reservoirs, houses, trenches (euripi), gardens, and surburban villas, and, along the distance which it traverses, the arches built, the mountains perforated, the valleys levelled, he [p. 1.148]will confess that there never was anything more wonderful in the whole world.”

The detailed description of the arrangements of the aqueduct will be better understood, after an enumeration of the principal aqueducts by which water was conveyed to Rome across the Campagna. Our knowledge of the subject is derived almost entirely from the treatise De Aquaeductibus Urbis Romae, by S. Julius Frontinus, who was curator aquarum (keeper of the aqueducts) under Nerva and Trajan. It should be observed that the Aquaeductus is often called simply Aqua. There were nine aqueducts in the time of Frontinus, of which four belong to the time of the republic, while five were built in the reigns of Augustus and Claudius.

    1. The Aqua Appia was begun by the censor Appius Claudius Caecus (to whom also Rome was indebted for her first great road), in B.C. 312. Its sources are mentioned by Frontinus as near the Via Praenestina, between the seventh and eighth milestones. But this appears to be a mistake, as its real source has been discovered in the reservoirs formed in the ancient quarries, now called latomie della Rustica, about 50 feet below the level of the ground. Perhaps we ought to read Via Collatina instead of Praenestina (Middleton, Ancient Rome, p. 466). Its termination was at the salinae, by the Porta Trigemina. Its length was 11,190 passus, for 11,130 of which it was carried under the earth, generally at a considerable depth; and for the remaining 60 passus, within the city, from the Porta Capena to the Porta Trigenmina, it was on arches. The distribution of its water began from the Clivus Publicius. (Frontin. 5; Liv. 9.29; Diod. 20.36; Aur. Vict. Vir. Illust. 34, who confounds it with the Anio.) Its subterranean specus has been discovered in several places in Rome, especially at one point where it passes through the old tufa quarries in the Aventine near the church of S. Saba; its line near this point is now traversed by the modern Via di Porta (Middleton; l.c.).
  • 2. The Anio Vetus was commenced forty years later, B.C. 272, by the censor M‘. Curius Dentatus; but as the time of the censorship expired before the work was completed, duumviri aquae perducendae were appointed, and the aqueduct was finished by M. Fulvius Flaccus, one of the duumvirs, the other having died shortly after his appointment. The expense was defrayed out of the spoils taken from Pyrrhus. The water was derived from the river Anio, above Tibur, at a distance of ten Roman miles from the city; but, on account of its windings, its actual length was forty-three miles (ita exigente libramento, Front.), of which length less than a quarter of a mile only (namely, 221 passus) was above the ground. There are considerable remains of this aqueduct below the Claudian aqueduct, near the Porta Maggiore, and other pieces of the specus and remains of large cisterns were discovered while laying out the new streets Principe Amadeo, Carlo Alberto, and Napoleone III. (Middleton, p. 467), and also in the neighbourhood of Tivoli, which was supplied with its water. It was built of blocks of peperino stone, and the water-course was lined with a thick coating of cement. (Front. 6; Aur. Vict. Vir. Ill.. 43.)
  • 3. The Aqua Marcia, one of the most important of the whole, was built by the praetor Q. Marcius Rex, by command of the senate, in B.C. 144. The want of a more plentiful supply of water had been long felt, especially as that furnished by the Anio Vetus was of such bad quality as to be almost unfit for drinking; and, in B.C. 179, the censors M. Aemilius Lepidus and M. Flaccus Nobilior had proposed the erection of a new aqueduct; but the scheme had been defeated, in consequence of Licinius Crassus refusing to let it be carried through his lands. (Liv. 40.51, 7.) The two existing aqueducts had also fallen into decay by neglect, and had been much injured by private persons drawing off the water at different parts of their course. The senate therefore commissioned the praetor Marcius to repair the old aqueducts, and to build a third, which was named after him. According to Fenestella (ap. Front.), 180 million sesterces were voted for the purpose. Some writers have pretended that the original construction of this aqueduct is to be ascribed to Ancus Marcius, alleging a passage of Pliny (Plin. Nat. 31.41), and a medal of the Marcian gens, family Philippus, which bears on the obverse a head with the legend ANCVS, and on the reverse a representation of an aqueduct, with the letters AQVAMR (Aqua Marcia) between the arches, supporting an equestrian statue with the legend PHILLIPPVS: but those who know anything of the history of Roman family records will understand that this medal bears no evidence to the point in question, and is simply a perpetuation of two of the greatest distinctions of the Marcia gens, their alleged descent from Ancus, and the aqueduct which bore their name; and Pliny's opinion is simply one of his ludicrous blunders, arising probably from his confounding Marcius Rex with the king Ancus Marcius. (Eckhel, Doctr. Num. Vet. vol. v. p. 248.)

    Medal of the Marcia gens, recording the Aqua Marcia.

    This aqueduct commenced three miles south of the Via Valeria, thirty-six miles from Rome; its length was 61,710 1/2 passus, of which only 7463 were above ground; namely, 528 on solid substructions and 6935 on arches. It was high enough to supply water to the summit of the Capitoline Mount. It was repaired by Agrippa in his aedileship, B.C. 33 (see below, No. 5), and the volume of its water was increased by Augustus, by means of the water of a spring 800 passus from it: the short aqueduct which conveyed this water was called the Aqua Augusta, but is never enumerated as a distinct aqueduct. Pliny states that the water of the Aqua Marcia was the coldest and most wholesome of all which was brought to Rome; and Vitruvius and other writers refer to the excellence of the water as being proverbial. Considelable remains of it are still standing both above and below Tivoli. (Frontin. 7, 12; Plin. Nat. 31.41, who differs from Frontinus in some of the details Strab. v. p.240; Vitr. 8.3.1; D. C. 49.42; Plut. Cor. 1; Prop. 3.22, 24; [p. 1.149]Mart. 6.42, 18; Stat. Silv. 1.5, 25.) Its specus can be seen, where it passes over the arch built by Augustus below the specus of the Aqua Julia and Tepula (see No. 5).

  • 4. The Aqua Tepula, which was built by the censors Cn. Servilius Caepio and L. Cassius Longinus in B.C. 127, began at a spot in the Lucullan or Tusculan land, two miles to the right of the tenth milestone on the Via Latina. Its water was slightly warm, whence its name, tepula, a form of tepida. It was afterwards connected with
  • 5. The Aqua Julia. Among the splendid public works executed by Agrippa in his aedileship, B.C. 33, was the formation of a new aqueduct, and the restoration of all the old ones. From a source two miles to the right of the twelfth milestone of the Via Latina, he constructed his aqueduct (the Aqua Julia) first to the Aqua Tepula, in which it was merged as far as the reservoir (piscina) on the Via Latina, seven miles from Rome. From this reservoir the water was carried along two distinct channels, on the same substructions (which were probably the original substructions of the Aqua Tepula, newly restored), the lower channel being called the Aqua Tepula, and the upper the Aqua Julia; and this double aqueduct again was united with the Aqua Marcia, over the watercourse of which the other two were carried. The arch bearing the three aqueducts, where it entered the city, is now the Porta S. Lorenzo; and the rebuilding of this part of the aqueduct by Augustus in B.C. 5 is recorded by an inscription on the side of the specus of the Aqua Julia (A in cut). Other restorations were made by Titus in A.D. 79, recorded in an inscription on the frieze below (B in cut); by Severus in 196; and by Caracalla in 212. The restoration by Caracalla is recorded in an inscription, to make room for which the moulded pediment has been cut away (C in cut).

    Arch built by Augustus where the three Aqueducts,
    Julia, Tepula,
    and Marcia, pass over a road, now the Porta S. Lorenzo. (From Middleton.)
    A. Original inscription by Augustus.

    B. Inscription recording restoration y Titus.

    C. Inscription added by Caracalla.

    D. Peperino arch of the Aqueduct.

    E. F, G. Specus of the Marcia, Tepula, and Julia.

    H. Part of one of the towers of Aurelian's Wall.

    In Rome itself the three specus were separated and carried in different directions. A section of the three specus is given below (see p. 153). The whole course of the Aqua Julia, from its source, amounted to 15,426 passus, for 7000 of which its course was above ground, partly on massive substructions and partly on arches. (Frontin. 8, 9, 19.)

  • 6. The Aqua Virgo was also built by Agrippa in his aedileship. In the same year, Agrippa, according to Pliny (Plin. Nat. 36.121), erected for public use 700 basins or pools (lacus), 500 fountains (salientes), 130 castella, adorned with 300 statues and 400 marble columns. The main object of the Aqua Virgo was to supply the baths of Agrippa. From a source in a marshy spot by the eighth milestone on the Via Collatina, it was conducted by a very circuitous route, chiefly under the ground, to the M. Pincius, whence it was carried on arches to a spot opposite the east side of the Pantheon. Its length was 14,105 passus, of which 12,865 were underground; in its subterranean course it received the water of numerous springs; and its water was as highly esteemed for bathing as that of the Aqua Marcia was for drinking. It is one of the aqueducts on the left bank of the Tiber which are still in use, though on a [p. 1.150]much diminished scale. (See p. 151b.) The origin of its name is variously explained. (Frontin. 10; D. C. 54.11; Plin. Nat. 31.42; Cassiod. Var. 7.6; Ov. Tr. 3.12, 22; Mart. 5.20, 9, 6.42, 18, 11.47, 6.) “A well-preserved piece of the ancient specus can be seen below the level of the street, in the court of No. 12, Via del Nazzareno, behind the Trevi fountain. The arches themselves, which are of peperino, are buried, but the specus of massive travertine, decorated with an entablature, is visible, and is perfectly preserved. On both sides of the frieze is an inscription recording that this part was rebuilt by Claudius in A.D. 52.” (Middleton, p. 471.)
  • 7. The Aqua Alsietina (sometimes called also Aqua Augusta), on the other side of the Tiber, was constructed by Augustus from the Lacus Alsietinus (Lago di Martignano), which lay 6500 passus to the right of the fourteenth milestone on the Via Claudia, to the part of the Regio Transtiberina below the Janiculus. Its length was 22,172 passus, of which only 358 were on arches, its level being lower than that of any other aqueduct; and its water was so bad that it could only have been intended for the supply of Augustus's Naumachia, and for watering gardens. Its reservoir was 1800 feet long by 1200 wide. (Frontin. 11.)
  • 8, 9. The two most magnificent aqueducts were the Aqua Claudia and the Anio Novus (or Aqua Aniena Nova), both commenced by Caligula in A.D. 38, and finished by Claudius in A.D. 52. The water of the Aqua Claudia was derived from two copious and excellent springs, called Caerulus and Curtius, near the thirty-eighth milestone on the Via Sublacensis, and it was afterwards increased by a third spring, Albudinus, and by the waters of the Augusta. Its water was reckoned the best after the Marcia. (Frontin. 13, 14: cf. Suet. Cal. 21, Claud. 20; Lamprid. Alex. 30.) Its length was 46,406 passus (nearly 46 1/2 miles), of which 9567 were on arches and 609 on substructions. Of a still greater length was the Anio Novus, which began at the forty-second milestone, on the Via Sublacensis, being taken from a dam constructed in the bed of the river, and which received in addition, at the thirty-eighth milestone, opposite the sources of the Aqua Claudia, a stream called the Rivus Herculaneus. It was the longest and the highest of all the aqueducts, its length being nearly 59 miles (58,700 passus, of which 9400 were above ground), and some of its arches 109 feet high (Frontin. 15). In the neighbourhood of the city these two aqueducts were united, forming two channels on the same arches, the Claudia below and the Anio Novus above. An interesting monument connected with these aqueducts is the gate now called Porta Maggiore, which was originally a magnificent double arch, by means of which the aqueduct was carried over the Via Labicana and the Via Praenestina. The Porta Labicana was blocked up by Honorius; but the arch has been lately cleared of his barbarous constructions. Over the double arch are three inscriptions, which record the names of Claudius as the builder, and of Vespasian and Titus as the restorers of the aqueduct. The annexed cut (after Hirt) represents a restored section. By the side of this arch the aqueduct passes along the wall of Aurelian for some distance, and then it is continued upon the Arcus Neroniani or Caelimontani, which were added by Nero to the original structure, and which terminated

    Section of the Porta Maggiore at Rome: a. the Aqua Claudia; b. the Anio Novus; c. openings to give vent to the air.

    at the temple of Claudius, which was also built by Nero, on the Caelius, where the water was probably conveyed to a castellum already built for the Aqua Julia, and for a branch of the Aqua Marcia, which had been at some previous time continued to the Caelius. The Arch of Dolabella, erected B.C. 10, was used as a foundation for a large reservoir constructed at that point. The ruined arches of the Claudian aqueduct still extend for many miles across the Campagna.

These nine aqueducts were all that existed in the time of Frontinus, who thus speaks of them collectively, in terms which can hardly be thought exaggerated: “Tot aquarum tam multis necessariis molibus pyramidas videlicet otiosas compares, aut inertia sed fama celebrata opera Graecorum.” It has been calculated that these nine aqueducts furnished Rome with a supply of water equal to that carried down by a river thirty feet broad by six deep, flowing at the rate of thirty inches a second. The total water supply of Rome has been estimated at 332,306,624 gallons a day, or, taking the population at a million, 332 gallons a head. 40 gallons a head is now considered sufficient. But the demands for public purposes and for irrigation were large. There was also another aqueduct, not reckoned with the nine, because its waters were no longer brought all the way to Rome. This was the Aqua Crabra, which had its [p. 1.151]source near that of the Julia, and which was originally carried right through the Circus Maximus; but the water was so bad that Agrippa would not bring it into the Julia, but abandoned it to the people of the Tusculan land; hence it was called Aqua Damnata. Cicero had to pay to the city of Tusculum an acknowledgment for its use. At a later period, part of its water was brought into the Aqua Julia, but it was again cut off from the Julia by Frontinus, and restored to the people of Tusculum (Cic. Agr. 3.2, 9; Balb. 20, 45; Fam. 16.18, 3; Frontin. 9). It is now made use of in its course through the Campagna for watering cattle and sheep (Burn, Rome, p. 359).

There are still two aqueducts of later construction to be added to the list.

  • 10. The Aqua Trajana was brought by Trajan from the Lacus Sabatinus (now Bracciano), to supply the Janiculus and the Regio Transtiberina. Its construction is recorded on coins of gold, silver, and bronze, of the years 110 and 111 A.D. (Eckhel, Doctr. Num. Vet. vi. pp. 425, 428). Trajan also restored and improved the other aqueducts, especially the Anio Novus (Frontin. 92, 93). The castellum of this aqueduct on the Janiculan hill is shown on the coins of Trajan. The aqueduct was restored by Belisarius, after it had been injured by the Gothic king Vitiges in A.D. 537.
  • 11. The Aqua Alexandrina was constructed by Alexander Severus, A.D. 226; its source was in the lands of Tusculum, about fourteen miles from Rome, between Gabii and the Lake Regillus. Its small height shows that it was intended for the baths of Severus, which were in one of the valleys of Rome. (Lamprid. Alex. Sev. 25; Fabretti, Diss. 1.23.) Parker, from an inscription of Hadrian found on its collecting reservoir, attributes Fabretti's Alexandrina to Trajan or Hadrian, holding the real Alexandrina to have been a branch from the Anio Novus.
There may have been some other aqueducts constructed at a later time, since Procopius (B. G. 1.19) mentions fourteen as still preserved in Rome in his time; but there is difficulty in making up this number. He seems to have included as separate aqueducts some which were only branches of those already mentioned. Thus we read of the Aqua Septimiana, built by Septimius Severus, which was, perhaps, only a branch of the Aqua Julia, formed by the emperor to bring water to his baths (Fabretti, Diss. 3.285). The Aqua Algentia seems to have been a name invented from a corrupt reading of Alsietina (Middleton, p. 475). Other authorities give a still larger number of aqueducts. Thus the Epilogus to the Notitia mentions the Ciminia, the Severiana, and the Antonia (Antoniniana), and makes the whole number nineteen.

Great pains were taken by successive emperors to preserve and repair the aqueducts. From the Gothic wars downwards, they have for the most part shared the fate of the other great Roman works of architecture, their situation and purpose rendering them peculiarly exposed to injury in war; but still their remains form the most striking features of the Campagna, over which their lines of ruined arches, clothed with ivy and the wild fig-tree, radiate in various directions. Three of them still serve for their ancient use; and these three alone, according to Tournon, supply the modern city with a quantity of water much greater than that which is furnished to Paris by the Canal de l'Ourcq, for a population six times as large. They are: (1.) The Acqua Vergine, the ancient Aqua Virgo, which was restored by Pope Pius IV. and further embellished by Benedict XIV. and Clement XIII. The chief portion of its waters gush out through the beautiful Fontana di Trevi, but it also supplies the fountains in the Piazza di Spagna and the Piazza Navona, together with ten smaller ones, and the greater part of the lower city. (2.) The Acqua Felice (A.D. 1587), named after the conventual name of its restorer, Sixtus V. (Fra Felice), probably brings the waters from the spring of the Alexandrina, partly on the piers of the Claudia. It supplies twenty-seven public fountains, and the eastern part of the city. (3.) The Acqua Paola, the ancient Trajana and Alsietina, now united and restored by Paul V. (1611), supplies the Trastevere and the Vatican, and feeds, among others, the splendid fountains before St. Peter's. Besides these, the Acqua Marcia-Pia (1870) brings to Rome in pipes the old Aqua Marcia, which has now regained its ancient repute. Of the ruins of the other aqueducts the most extensive, within Rome, are those of the Arcus Neroniani and of the Aqua Crabra; the most interesting are the Porta Maggiore, with the two channels of the Aqua Claudia and Anio Novus (see p. 150), and the remains of the triple aqueduct of Agrippa, passing over a road, and resting upon an arch, now the Porta S. Lorenzo, already described (see p. 149).

The magnificence displayed by the Romans in their public works of this class was by no means confined to the capital; for aqueducts more or less stupendous were constructed by them in various and even very remote parts of the empire,--at Athens, Corinth, Catana, Salona, Nicomedia, Ephesus, Smyrna, Alexandria in the Troad, Syracuse, Metz, Clermont in Auvergne, Nîmes (the Pont du Gard; see below), Lyon, Evora, Merida, and Segovia. Those at Ephesus and Alexandria were built by Hadrian and Herodes Atticus, and that at Athens was commenced by Hadrian and finished by Antoninus Pius, who also built those at Corinth and Nicomedia. That at Evora, which was built by Quintus Sertorius, is still in good preservation ; and at its termination in the city has a very elegant castellum in two storeys, the lower one of which has Ionic columns. Merida in Spain, the Augusta Emerita of the Romans, who established a colony there in the time of Augustus, has among its other antiquities the remains of two aqueducts, of one of which thirty-seven piers are standing, with three tiers of arches; while of the other there are only two which form part of the original constructions, the rest being modern. But that of Segovia, for which some Spanish writers have claimed an antiquity anterior to the sway of the Romans in Spain, is one of the most perfect and magnificent works of the kind anywhere remaining. It is entirely of stone, and of great solidity, the piers being eight feet wide and eleven in depth; and, where it traverses a part of the city, the height is upwards of a hundred feet, and it has two tiers of arches, the lowermost of which are exceedingly lofty. The Pont du Gard, carrying an aqueduct across the valley and [p. 1.152]stream of the Gardon into Nemausus (Nîmes), consists of two tiers of noble arches, surmounted by a tier of small arches which bear the specus, the whole height of the three tiers being about 155 feet.

It will be observed that when the pacification of the Campagna permitted Rome to look afield for a supply of water, the first great work constructed was entirely underground, except for a short distance inside the walls. Moreover

Aqueduct near Nemausus, now called the Pont du Gard.

we may divide the aqueducts described by Frontinus into those at a low level, intended to supply the low-lying districts and for the most part carried underground, and those at a high level, designed to reach the higher parts of the city; and in the latter alone were arcades and substructions largely employed. Frontinus (18) says that five reached the highest parts of the city, and he gives them in the following order: 1. Anio Novus, the highest of all. 2. Claudia. 3. Julia. 4. Tepula. 5. Marcia. Then follow the lower, constructed to a great extent underground. 6. Anio Vetus. 7. Virgo. 8. Appia. 9. Alsietina, the lowest of all, supplying the district beyond the Tiber and the lowest spots. The aquae from the upper waters of the Anio (Anio Vetus, Marcia, Anio Novus, Claudia) made a considerable détour southwards to follow the high ground by Pedum, Labicum, and Frascati, and then cross the Campagna more directly for Rome, following more or less closely the course of the Via Latina.

Why did the Romans waste so much labour and money on works the purpose of which might have been effected much more economically by the simple plan of laying pipes along the ground, with which they were certainly well acquainted? (Vitr. 8.7.) Aqueducts, it is true, are often constructed in modern times in a suitable country; as, for instance, the New River for the supply of London, and the aqueduct of the Croton River for New York: but surely a modern engineer, if asked to convey water from the upper course of the Anio across the low-lying parts of the Campagna to the tops of the Seven Hills, would, like the engineer of the new Acqua Marcia-Pia, propose to carry out the undertaking by laying down pipes. This question was formerly answered by saying that the Romans did not know that “water finds its own level.” But this is contradicted by the express statement of Latin authors (Plin. Nat. 31.57, “subit altitudinem exortus sui ;” Vitr. 8.6.5, and 7.6, where he describes the application of the principle to an aqueduct), by the whole arrangements for the distribution of the waters of the aqueducts to the upper rooms of their houses, and from the very existence of their numerous fountains. As a decisive ocular demonstration we give a section of one of the many fountains still existing at Pompeii. Possibly, however, they did not recognise that the law would hold over so extended an area. Frontinus at any rate, an excellent authority on Roman engineering, theoretical and. practical, does not contemplate its applicability.

Section of a fountain at Pompeii. Section of a fountain at Pompeii. a, a. The ascending pipe.

b, b. The basin, made of blocks of travertine.

Indeed it is very doubtful whether Roman engineers would have been found equal to the task of conveying by an underground channel a large stream of water subject, like that from the upper Anio, to a high pressure. Their conduits were always pierced by shafts at intervals of one or two actus, designed to avoid the supposed danger of the walls being burst by the compressed air inside. Now these shafts, sunk in the low-lying parts of the Campagna, would of course make it impossible to force the water to the tops of the hills; they were confessedly designed to relieve the pressure: and engineers were probably led to use them, and thus explain their use by the bursting of unpierced conduits conveying water at high pressure. If they had recourse to pipes, the joints would present great difficulties, and probably for such large volumes of water iron pipes would alone be sufficiently strong, and the casting of pipes of such dimensions would have been beyond their power. Moreover, as Mr. Middleton observes (p. 453), “the calcareous deposit with which water from the neighbourhood of Rome so rapidly encrusts pipes and water-channels made it doubly convenient [p. 1.153]to employ channels which were always readily accessible, and could be cleared out without any difficulty.”

A strip of land 15 feet wide, marked at intervals by cippi or boundary-stones, was left on either side of the aqueduct, upon which no encroachments were allowed under penalty of a heavy fine. All trees were in particular forbidden to be planted, lest their roots should injure the substructions or arches of the aqueduct (Frontin. 127). The cippi or boundary-stones seem to have been first placed by Augustus, but were discontinued by the later emperors, since of the 31 cippi still extant, 22 bear the name of Augustus, three of Tiberius, two of Claudius, and the other five are restorations (Lanciani, I Comentarii di Frontino, p. 345).

We proceed to describe in detail the construction and arrangements of Roman aqueducts. There are three matters to be considered: the source from which the water was derived; the aqueduct itself, by which it was conveyed; and the reservoir in which it was received, and from which it was distributed for use.

(1.) The Sources.--It is unnecessary to follow Vitruvius into the minute rules which he lays down for the discovery of springs, where they were not naturally visible, and for testing the quality of the water: it is enough to refer to his statements as showing the importance attached to these points. (Vitr. 8.1.) It was also necessary that the springs should have such an elevation, as that, after allowing for the fall necessary to give the channel its proper inclination, the water should enter the final reservoir at a sufficient height to permit of its distribution for public and private use; for there were no engines used, as in modern waterworks, to raise the water to a higher elevation than that to which it rose of itself. When the source had been fixed upon, whether it was an open spring (fons), or one got at by sinking a well (puteus), a head was dug for the water, and enclosed with a wall; and, if necessary, the supply was increased by digging channels from neighbouring springs: the rules for these operations also are minutely laid down by Vitruvius (8.7, s. 6, § § 12-15). Such a reservoir was called piscina, sometimes piscina limaria (Frontin. 15), in which the water might deposit any sediment it contained.

(2.) The Channel (specus, sometimes canalis), or Aqueduct itself.1--In order to convey the water from its source to its destination, a channel was constructed, having a slight and, as nearly as possible, a uniform declivity. An elaborate description of the means adopted to secure this object is quite needless for readers of the present day, as they were almost precisely similar to those with which we are familiar in our railways: hills were pierced through by tunnels, and valleys crossed either by solid substructions or arches of masonry, according to the height required; and of these arches there were often two tiers, and sometimes even three. The material employed was generally stone (usually travertine or peperino), but sometimes rubble faced with brickwork (as in the Arcus Neroniani, the Anio Novus, the Alexandrina) or with opus reticulatum (as in the Anio Novus). The channel itself (specus, canalis) was a trough of brick or stone, lined with very hard cement (opus signinum), made of lime, pozzolana, and pounded pottery or brick. and covered with a coping, which was almost always arched, and the bottom of the channel was also curved. The water either ran directly through this trough, or it was carried through pipes laid along the trough. When the channel was carried beneath the surface, if the hill through which it passed was of rock, it was merely cut in the rock; but if of earth or sand, it was constructed of blocks of stone.

The construction of the specus will be seen from the annexed drawing, which represents a section of the triple aqueduct of Agrippa. (See above, p. 149.)

Section of the specus of the triple Aqueduct of Agrippa. (From Middleton.) A, B, C. Specus of the Aquae Julia, Tepula, and Marcia. The top and bottom of each is of travertine, the sides of tufa or peperino: they are lined with opus signatum.

D. Peperino arch.

E. Specus of the Aqua Julia at another point, where it has been restored in concrete and brick.

The object of covering the specus was to exclude the sun and rain, and other obstructions; but it was necessary to provide a vent for the air, which otherwise, they thought, would have been compressed to such a degree as to burst the walls or roof of the specus. The vent-holes (spiramina) were made at regular intervals in the roof of the specus, or, when another channel passed over it, in the side. They are represented in the sections, given above, of the Aqua Claudia and Anio Novus (p. 150). To ventilate the subterranean channel of an aqueduct, a shaft (puteus) of masonry was carried to the surface of the ground at intervals of an actus, or 120 Roman feet (or two actus, [p. 1.154]according to Pliny, who calls them lumina), as shown in the following woodcut (after Hirt),

Shaft for ventilation of an Aqueduct. Shaft for ventilation of an Aqueduct. a, the water-course; b, steps giving access to it; c, the shaft; d, e, section of the specus and shaft; f, transverse section of them.

which represents the plan, longitudinal section, and transverse section of part of a rivus subterraneus, the ruins of which still exist at Palmyra.

The rivus subterraneus possessed the advantage over the aquaeductus of being less exposed to variations of temperature, and more secure from injury; on the other hand, it was of course more difficult to get at when it required repairs. A reference to the account of the Roman aqueducts given above will show how large a portion of them were subterranean.

Instead of, or within, the specus, pipes (fistulae, tubuli) were often used for the passage of the water. They were of lead, or terra-cotta (fictiles), and sometimes, for the sake of economy, of leather. The rules which Vitruvius lays down apply particularly to leaden pipes, although he gives the preference to the earthen ones, chiefly on the ground that the water which passed through them was more wholesome. The pipes were made in lengths of not less than ten feet, and of various widths, which were denominated in the manner explained under FISTULA They were cemented together at the joints, which in earthen pipes were made to overlap; and when the water was first let in, ashes were mixed with it, in order that they might settle in the joints and stop them more completely. The use of pipes permitted variations to be made in the construction of the aqueduct: namely, the water could be carried round instead of through a hill, if the circuit was not too great; and in very wide valleys the costly structure of arches could be dispensed with. In this case, a low horizontal substruction was made across the bottom of the valley, and the pipe was brought down the one slope, along this substruction, and up the opposite slope, to a height of course somewhat less than that of the opposite side. The horizontal part of the pipe across the bottom of the valley (venter) had ventilating openings for the escape of the air. At the bendings, instead of the pipe, an elbow was bored in a solid piece of stone, into which the ends of the adjacent pieces of pipe were securely cemented. (For further details, see Vitruvius.) In those places where the pipes were laid on the surface, reservoirs were sometimes made, at intervals of 200 actus (24,000 feet), in order that, if a part of the pipe needed repair, the supply of water might not be entirely cut off. The advantage in the use of pipes, according to Vitruvius, was the facility of repairing them.

The slope (fastigium) on which the aqueduct was built, in order to give the water a proper fall (libramentum), ought not, says Vitruvius (8.6), to be less than half a foot in every 100 feet (1 in 200); but Pliny only allows a siciicus (a quarter of an inch) in 100 feet. The great circuit which most of the aqueducts of Rome made, was taken chiefly (as is the case with the New River) to prevent the too rapid descent of the water. There is, however, a considerable variation in their declivities: for example, the Aqua Marcia and the Aqua Claudia, though of such different heights at Rome, have their sources at the same elevation.

Besides the reservoir or piscina at the source of the aqueduct, there were similar reservoirs at convenient points in its course, especially at the middle and end. The construction of these reservoirs will be understood from the following woodcut, which represents a restored section of one which still exists.

Piscina, or reservoir of an Aqueduct.

The water flowed from the aqueduct a into the first upper chamber, thence down and up again through the openings b, c, e, into the second upper chamber, out of which it passed into the continuation of the aqueduct f, having deposited its sediment in the two lower chambers, which could be cleaned out by the door d. The piscina was not always vaulted: Hirt, from whose work the above cut is taken, gives also an engraving of an open piscina. These reservoirs were not always used: for example, the Aqua Virgo and the Alsietina were without them. They were especially necessary when the water was conveyed through pipes. They were also used as reservoirs for the supply of the neighbouring country, chiefly for the purposes of irrigation.

The details which we have now been noticing are minutely described by Frontinus, and by Vitruvius (8.7, s. 6), and briefly by Pliny (Plin. Nat. 31.57).

(3.) The Termination of the Aqueduct, and the Arrangements for the Distribution of its Water.--The water, when it reached the walls of the city, was received in a vast reservoir called castellum aquarum, which formed the head of water. (Vitr. 8.6; Plin. Nat. 36.121; Frontin. 35; Dig. 43, tit. 20.) The more ancient name in use, when the aqueducts were first constructed, was dividiculum. (Festus, s. v.) From this principal castellum the water flowed into other castella, whence it was distributed for public and private use. The term castellum, [p. 1.155]is sometimes also applied to the intermediate reservoirs already mentioned.

The chief castellum was, externally, a highly decorated building: for example, that of Hadrian, at Athens, was adorned with Ionic pillars, and that at Evora, in Portugal, had the form of a circular temple. Internally, there was generally one vast chamber, lined with hard cement (opus signinum), with a vaulted roof supported by massive pillars, into which the water flowed from the aqueduct, and from which it was conducted through pipes of fixed dimensions into three smaller reservoirs, which were, however, so arranged, that the middle one was only supplied from the overflow of the other two. Of these three reservoirs, the two outer supplied respectively the public baths and the private houses, and the middle one the public ponds and fountains (lacus et salientes); so that, in case of a deficient supply for useful purposes, none would be wasted on the fountains: the arrangement also enabled a proper account to be kept of the quantity supplied for private use, for the protection of the revenue derived from this source. (Vitr. 8.7, s. 6, § § 1, 2.)

The minor castella, which “received the water from this chief head, were distributed over the city, in such a manner that the Aqua Appia supplied seven regiones by means of twenty castella; the Anio Vetus, ten regiones through thirty-five castella; the Marcia, ten regiones through fifty-one castella; the Tepula, four regiones through fourteen castella; the Julia, seven regiones through seventeen castella; the Virgo, three regiones through eighteen castella; the Claudia and the Anio Vetus, ninety-two castella.” (Frontin. 79-86.) For an account of the parts of the city supplied by the different aqueducts, see Becker, Handb. d. Röm. Alterth. vol. i. pp. 707, 708.

The ruins of the magnificent castellum of the Aqua Julia, built by Alexander Severus on the Esquiline, may be seen in the Piazza Vittorio Emmanuele. “It is shown with some minuteness on medallions of Alexander Severus. (See Froehner, Med. Rom. p. 169.) It was excavated, and careful drawings of it were made by some Prix de Rome students in 1822. It was again and more completely exposed in 1877, and no lead pipes were found leading from it, as would have been the case if it had been an ordinary castellum for the erogatio. The so-called Trophies of Marius, made in the reign of Domitian, were set on the exterior of this building, whence they were moved in the 16th century to the top of the Capitoline stairs.” (Middleton, p. 458.) It is now much dilapidated, but was tolerably entire about the middle of the 16th century, as may be seen by the drawing published by Gamucci (Antichità di Roma, iii. p. 133) from which this restoration is made. The ground-plan explains part of the internal construction, and shows the arrangement adopted for disposing of the superfluous water of an aqueduct. The general stream of water is first divided by the round projecting buttress into two courses, which subdivide themselves into five minor streams, and finally fall into a reservoir.

The castella were divided into two classes, the publica and privata.

The castella publica were again subdivided into six classes, which furnished water for the following uses:--(1) The Praetorian camp (castra); (2) the ponds and fountains (lacus et

Castellum of an Aqueduct, called the “Trophies of Marius.”

salientes); (3) the circus, naumachiae, and amphitheatres (munera); (4) the baths, and the service of certain important handicrafts, such as the fullers, dyers, and tanners (opera publica); (5) irregular distributions made by the special order of the emperor (nomine Caesaris); (6) extraordinary grants to private individuals by the favour of the prince (beneficia Caesaris). The distribution under each of these heads is described by Frontinus, who enumerates the various laws relating to water supply, Jus ducendae tuendaeque Aquae (Frontin. 3, 78).

The castella privata were, as the name implies, for the supply of private houses. When a supply of water from the aqueducts was first granted for private uses, each person obtained his quantum by inserting a branch pipe, as we do, into the main; which was probably the custom in the age of Vitruvius, as he makes no mention of private reservoirs, for which at first there was no occasion, as there was a constant supply of water. Indeed, in early times, all the water brought to Rome by the aqueducts was applied to public purposes exclusively, it being forbidden to the citizens to divert any portion of it to their own use, except such as escaped by flaws in the ducts or pipes, which was termed aqua caduca (Frontin. 94). But as even this permission opened a door for great abuses from the fraudulent conduct of the aquarii, who damaged the ducts for the purpose of selling the aqua caduca; and as the subsequent method of supply required the main-pipe to be punctured in too many places (Frontin. 27), a remedy was sought by the institution of castella privata, and the public were thenceforward forbidden to collect the aqua caduca, unless permission was given by special favour (beneficium) of the emperor (Frontin. 111). The castella privata were built at the joint expense of the families supplied by them; but they were considered as public property, and were under the control of the curatores aquarum (Frontin. 106). The right of water (jus aquae impetratae) did not follow the heir or purchaser [p. 1.156]of the property, but was renewed by grant upon every change in the possession (Frontin. 107).

The leaden cisterns, which each person had in his own house to receive the water laid on from the castellum privatum, were called castella domestica.

All the water which entered the castellum was measured, at its ingress and egress, by the size of the tube through which it passed. The former was called modulus acceptorius, the latter erogatorius. To distribute the water was termed erogare; the distribution, erogatio; the size of the tube, fistularum or modulorum capacitas, or lumen. The smaller pipes which led from the main to the houses of private persons, were called punctae; those inserted by fraud into the duct itself, or into the main after it had left the castellum, fistulae illicitae.

The erogatio was regulated by a tube called calix, of the diameter required (lumen), and not less than 12 digiti long (9 inches), attached to the extremity of each pipe, where it entered the castellum; it was probably of lead in the time of Vitruvius, such only being mentioned by him; but was made of bronze (aeneus) when Frontinus wrote, in order to check the roguery of the aquarii, who were able to increase or diminish the flow of water from the reservoir by compressing or extending the lead. As a further security, the calix was stamped with the owner's name as well as the capacity. There are two specimens of such calices in the Roman Museums; one in the Vatican, another in the Museo Kircheriano (Middleton, p. 455). Pipes which had no calix were termed solutae. Frontinus also observes that the velocity of the water passing through the calix, and consequently the quantity given out, could be varied according to the angle which the calix made with the side of the reservoir: its proper position was, of course, horizontal. (Frontin. 112, 113.)

It is evident how watchful an oversight must have been required to keep the aqueducts in repair, to regulate their use, and to prevent the fraudulent abstraction of their water. Under the republic, this office was discharged by the censors (Liv. 39.44), and when there were no censors by the aediles (Cic. Fam. 8.6); sometimes also by the quaestors (Frontin. 95, 96). Augustus first established the office of curator (or praefectusaquarum (Suet. Octav. 37), to which he appointed M. Agrippa, who held the office till his death in B.C. 12. A list of the curatores aquarum from Agrippa to Frontinus is given by the latter. They were all of consular rank, and hence we find them called subsequently consulares aquarum in place of their ancient name. They were under the Praefectus urbi. The duties of the office are minutely described by Frontinus (99), who seems, while he held the office, to have performed it with the utmost zeal : among other cares, he had plans and models made of the whole course of all the aqueducts (17, 64). The curatores aquarum had under them a large number of officials. They were attended outside the city by two lictors, three public slaves, a secretary, and other attendants.

In the time of Nerva and Trajan, a body of four hundred and sixty slaves were constantly employed under the orders of the curatores aquarum in attending to the aqueducts. They were divided into two families--the familia aquaria publica, established by Agrippa, and the familia aquaria Caesaris, added by Claudius; and they were subdivided into the following classes :--1. The vilici, 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, who had to remove and relay the pavement when the pipes beneath it required attention. 5. The tectores, who had charge of the masonry of the aqueducts. These and other workmen appear to have been included under the general term of AQUARII (Cod. 11, tit. 42 or 43, s. 10; Frontin. 116, 117.)

The following are the most important works on the Roman aqueducts :--Frontinus, de Aquaeductibus Urbis Romae, with the notes and plates of Polenus, Patav. 1722; Fabretti, de Aquis et Aquaeductibus Veteris Romae; Stieglitz, Archäologie der Baukunst; Hirt, Geschichte d. Baukunst; Platner and Bunsen, Beschreibung d. Stadt Rom; Becker, Handbuch d. Römischen Alterthümer, vol. i.; Canina, Storia dell' architettura Romana; Jordan, de urbium Romae et Const. aquaed., Bonn, 1844; Parker, Archæology of Rome; Burn, Rome and the Campagna. The most recent authorities are, Lanciani, Topographia di Roma Antica, I Comentarii di Frontino, Rome, 1880; Middleton, Ancient Rome in 1885, pp. 451-476.

[J.H.F] [W.S]

1 Though the word aquaeductus is applied generally to the whole structure, yet in its special and proper meaning it seems only to have signified that part of the work in which the water-channel was carried over a valley, on arches or on solid substructions: a channel on the surface of the ground was properly called rivus; and one beneath the surface, rivus subterraneus, or cuniculus.

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