12Roman Engineering

In this chapter strict chronology must be violated, and steps retraced, to discuss in specific detail something of what archaeology has to tell us about the most practical aspect of the Romans’ genius: their talent for engineering. This is best exemplified in roads, baths, aqueducts, and fortification-walls.

We have reached in our historical survey the end of Hadrian’s reign,A.D.138. By this date the main lines of the great consular roads leading from Rome had all been laid down, and later Emperors faced only the problems of maintenance, till the barbarians cut Rome’s lines of communication, and the moving of the administrative center to Milan, Ravenna, and Constantinople reduced their importance. The most recent archaeological investigation of Roman roads in Italy has concentrated on tracing the lines of major and minor Roman highways and the native tracks that preceded them, a work of great urgency, in view of the modernization which is rapidly changing the face of Italy, especially in the vicinity of Rome.

If we turn to Roman baths, like those of Caracalla in Rome, begun inA.D.211, we are back on the chronological track again, but we find that the last major archaeologicalwork upon them was done at the end of the last century, and that their chief interest today lies in the inspiration they have offered to modern architects.

As for aqueducts, the last important ancient one was built under the Emperor Alexander Severus, inA.D.226, but working back from that date we can profitably review the difficult and absorbing topographical work done in tracing the courses of the major aqueducts by a devoted Englishman and an American woman.

Finally we shall review the work of another Englishman in tracing the chronology and building techniques of ancient Rome’s last great fortification, Aurelian’s Wall, begun inA.D.271 and still in large part standing. Its alterations and repairs have been traced down to the middle of the sixth century of our era. The examples chosen should justify the Romans’ high reputation for engineering skill, and illuminate Roman history, at the same time underlining on the one hand our debt, for the facts we know and the inferences we draw, to the careful work of modern archaeologists, and on the other the catalytic effect, in the case of the baths, of Roman work upon our own architecture of the day before yesterday.

Fig. 12.1Roman road construction. (U.S. Bureau of Public Roads)

Roman roads (seeFig. 4.1) echoing to the measured tread of marching legions, had made a large contribution to unifying Italy by the time the last great consular highway, the Via Aemilia, opened up the Po valley from Ariminum to Placentia in 187B.C., but their work of carrying commerce and ideas was unceasing. Of course there were roads in Italy before the Romans: the name and route of the Via Salaria, from the salt-pans at the Tiber’s mouth up the valley into the Apennines, suggest that it must have been in use since prehistoric times. The Via Latina, named not for a Roman consul but for a people potent in central Italy until the Romans broke their league in 338B.C., must count as a pre-Roman road, and its winding course along the foothills must antedate the draining of the Pomptinemarshes and the laying down of the straight course across them from Rome to Tarracina and thence to Capua of theregina viarum, the queen of roads, the Via Appia. It bears the name of a Roman censor of 312B.C.This is the first of the great highways, and it deserves its fame for its bold conquest of natural obstacles, its arrow-straight course across the marshes, but its gravel surface was not replaced by stone pavement until 293B.C., and then only as far as the suburb of Bovillae. And its course, like that of many another Roman road, was not always so arrow-straight. In the hills behind Tarracina it followed the contours; it was not until Trajan’s time that another bold stroke of engineering cut through the high, rocky Pesco Montano to let the road pass by the more direct coastal route. (Some authorities hold that the Romans preferred straight roads because the front axles of their vehicles were rigid.) Trajan’s engineers showed their pride in their work by incising monumental Roman numerals, still visible, to mark thedepth of the cut every ten feet from the top down, until the road level was triumphantly reached at CXX.

Along the Appia, and the other consular roads radiating from Rome, traces of the ancient stone paving are occasionally preserved. The paving blocks are usuallyselce(flint), polygonal in shape and closely fitted without mortar. While most Roman roads prove on archaeological examination to consist of paving blocks laid in a trench and packed with earth andselcechips, it will be worthwhile to record the ideal method of laying a pavement—strictly speaking a mosaic pavement—as recommended by the architect Vitruvius, a contemporary of Augustus. The method illustrates the Roman engineer’s infinite capacity for taking pains.

After the field engineer (1 in the reconstruction,Fig. 12.1), assisted by the stake man (2), had aligned the road with hisgroma, he ran levels with thechorobates(3) with the roadman’s help (4). A plow (5) was used to loosen earth and mark road margins; then workmen dug marginal trenches (6) to the depth desired for the solid foundations. Laborers (7) shoveled loose earth and carried it away in baskets. The next step was to consolidate the roadbed with a tamper (8). Now the roadbed was ready for its foundation, thepavimentum(9), lime mortar or sand laid to form a level base. Next came thestatumen, or first course (10), fist-size stones, cemented together with mortar or clay, the thickness varying from ten inches to two feet. Over this was laid therudusor second course (11), nine to twelve inches of lime concrete, grouted with broken stone and pottery fragments. Next thenucleus, or third course (12), concrete made of gravel or coarse sand mixed with hot lime, placed in layers and compacted with a roller. Its thickness was one foot at the sides, eighteen inches at the crown of the road. Finally, thesummum dorsumor top course (13), polygonal blocks ofselcesix inches or more thick, carefully fitted and set in thenucleuswhile the concretewas still soft. Sometimes, when archaeologists have taken up a stretch of Roman road, they have found theselceblocks rutted on the under side: the economical contractors, happily untroubled by high-priced labor, had repaired their road by turning the worn blocks upside down. Standard curbs (14a and b) were two feet wide and eighteen inches high; paved footpaths (15a and b) often ran outside them. Conduits (16) under the curb, with arched outlets (17) opening beside the right of way, took care of draining surface water. Milestones (18) marked the distance from Rome and the name of the Emperor responsible for repairs. From the names of successive Emperors on milestones of the same road, archaeologists have calculated that the average life of a highway was thirty to forty years.

Two points should be emphasized: first, this represents an ideal method of construction, not often exemplified in practice; second, to a modern engineer a road like this would seem insufficiently elastic, a five-foot wall in the flat, too rigid for the stresses and strains to which it was subjected. Hence perhaps the frequent need for repairs, but Roman traffic was lighter than ours, and the very fact that we can write about the roads at all is a tribute to their durability. Upon roads like these, under the Empire, travelled the Imperial posting service, with relays of messengers, and post-houses where horses and carriages could be changed. Under exceptional conditions the Emperor Tiberius, using this service, once travelled 180 miles in a day, a rate of speed not equalled on European roads until the nineteenth century.

The next major road laid out after the Appia must have been the Valeria, which was needed for eastward communication via Tivoli with the new colony of Alba Fucens, founded, as we saw, in 303B.C.Archaeology has shown that in general the foundation of a colony precedes the laying down of the metalled military road. This is true of Cosa(foundation date of the colony, 273B.C.; probable date of the Via Aurelia which served it, about 241); of Ariminum (founded 268B.C.; reached by the Via Flaminia in 220), and of the Roman colonies in the Po valley;e.g., Bononia (Bologna: founded 189B.C.; reached by the Via Aemilia after 187). The full extension of the Via Valeria beyond Alba to the Adriatic had to await the pacification of the Samnite tribes of central Italy and the granting of citizenship to Italians after the “Social” War, in 89B.C.Milestones on this last stretch belong to Claudius’ reign (A.D.41–54).

A recent (1957) survey of the central section of the Valeria by the Dutch scholar C. C. Van Essen illustrates the methods and results of archaeologists working in the field with topographical problems. Faced with the palimpsest of more than two millennia overlying the road he wanted to trace, Van Essen paid particular attention to such roadmarks as Roman milestones; ancient tombs (which regularly lined Roman roads in the vicinity of towns); supporting walls, in Roman headers-and-stretchers; rock-hewn causeways; bridges, where Roman materials and workmanship can be distinguished from modern (as has been recently done for the bridges of the Via Flaminia by Michael Ballance of the British School at Rome; there the striking thing is the predominance and good quality of the work done under Augustus, who had a vested interest in assuring efficient communications with his veterans dispersed in colonies in north Italy). Stretches of ancient pavement are rare on the Valeria, having been destroyed by medieval and modern resurfacing, by the plow, and by torrents and earthquakes, but the trench in which it was bedded can often be distinguished on air photographs. What struck Van Essen chiefly was the frequency with which the ancient Via Valeria would run straight on, with steep gradients, where the modern road resorts to sweeping curves or hairpin bends. Ancient vehicles, the heaviest of which were perhaps only a quarter the weight of a modern light Europeancar (Roman wagon, perhaps 440 pounds; Volkswagen, 1650), and scarcely ever carried loads of over 1100 pounds, would be less troubled by steep gradients than a modern heavy truck. Even so, at Tagliacozzo, about six miles on the Rome side of Alba Fucens, the grade is so steep that Van Essen supposes the ancient inhabitants hired out oxen to help the straining horses on the upslope. Van Essen noted that the telegraph lines, following the comparatively straight course of the ancient road, often gave a clue to its presence. The ancient sixty-eighth milestone of the Valeria, found, as we saw, within the walls of Alba Fucens, provides a good comparison of the respective lengths of the ancient and the modern roads. Since the Roman mile (4861 English feet) was slightly shorter than the English, sixty-eight Roman miles corresponds to slightly over sixty-two English miles, whereas the modern Via Valeria covers about 113 kilometers, or approximately seventy miles, to reach Alba.

Archaeologists have not confined their interests to the great consular roads. Minor highways in areas away from the main stream of traffic are often more rewarding, since they tend to be better preserved, and offer some chance to trace the pre-Roman systems that underlie or intersect them. The district just north of Rome has been surveyed in this way by members of the British School at Rome since 1954, only just in time, for there prevails in this region a situation analogous to the rapid disappearance of Indian remains in the American West with the building of the great hydroelectric dams. In the country north of Rome, since World War II, there has been an extensive program of land expropriation, reclamation, and resettlement of small farmers, an excellent thing for rehabilitating the Italian peasantry, but fatal for archaeological remains, since the plan involves the use of the deep plow, an ideal instrument for obliterating traces of ancient roadways. Thus it is that members and friends of the British School, spurred on by the Director,John Ward Perkins, a worthy successor of the indefatigable Thomas Ashby, are to be seen braving wind and weather as they scour the countryside for Roman and pre-Roman roads from Veii to beyond Cività Castellana, armed with large-scale maps, air photographs, and brown paper bags for collecting the potsherds which are the evidence of ancient roadside habitation.

The British School’s most significant recent work has been carried on from Nepi, a Roman colony allegedly of 383B.C., twenty-eight miles north-northwest of Rome, and Falerii Novi, about four miles farther north. Falerii Novi was built by the Romans from the ground up in 241B.C.to house the inhabitants of Falerii Veteres (Cività Castellana) a hostile native Faliscan center, which the Romans completely destroyed. But the old city must have been resettled, for ruts in the third centuryB.C.road connecting the new city with the old are not of standard Roman width, and were probably made by Faliscan wagons. Thecardoof the new settlement is formed by a new road connection with the south, the Via Amerina (Fig. 12.2); in the course of exploring this the British archaeologists found traces from which the older road system (Fig. 12.3) which it partially supplanted, may be inferred. At Torre dell’ Isola, just north of Nepi, for example, they found, by the wall of a medieval castle, sherds with the cord-impressed chevrons characteristic of Villanovan ware, and part of one of the portable hearths which we met first in the primitive hut on the Palatine in Rome. These sherds provide evidence for habitation here at least as early as on the Palatine. The discovery of similar sherds within the walls of Etruscan Veii suggests a people inferior culturally to the Etruscans, and probably living in subjection to them.

Fig. 12.2Roman roads of theager Faliscus. (Papers Brit. Sch. at Rome12 [1957], p. 68)

These people were the Faliscans. Their settlements must have required road connections, especially between their chief city, old Falerii, and Veii, with which it was allied. These roads the British archaeologists have identified indeep cuttings, identified as pre-Roman by inscriptions in Etruscan characters. (Faliscan was a dialect of Latin, but Etruscan inscriptions occur.) These earliest cuttings, sometimes nearly fifty feet deep, are driven impressively through cliffs, cut downward from the surface in a succession of working levels to match the slope of the finished road, with careful attention paid to drainage. Pre-Roman stone piersprobably carried timber bridges, but most of the roads are mere ridgeway tracks, not unlike the medieval and modern farm tracks still to be found in the district. The Faliscans were apparently capable of ambitious engineering, but were driven by poverty to avoid it. The Romans used Faliscancuttings when they found it convenient, it being their way to take things as they found them, introducing modifications only to the minimum extent necessary to suit their own needs.

Fig. 12.3Faliscan roads of theager Faliscus. (PBSR,loc. cit., p. 105)

The most interesting and the most certainly identified Faliscan roads discovered in the British survey are in the neighborhood of Grotta Porciosa, a fortified site about four miles north-northeast of Cività Castellana and a mile and a half west of the Tiber. It controlled the ridge between two gorges, a natural route for a cross-country road between the Tiber and the towns of Gallese, Corchiano, and Cività Castellana. In these towns the Romans had no interest: the two main Roman roads in this area run not cross-country but north and south, the Via Flaminia close to the Tiber, the Via Amerina on the high ground five or six miles to the west. These roads bypassed all the towns just mentioned. But the cross-country tracks, on which the local inhabitants would travel, are visible both in air-photographs and on the ground, where they show no trace of Roman paving. At Grotta Porciosa itself, excavation would be required to reach the early Faliscan level; the majority of sherds found is local black glaze of a quite late pre-Roman period (mid-third centuryB.C.).

What is most striking about the British results is the contrast they point up between native and Roman. Where the native tracks usually follow the line of least resistance, the Roman Via Amerina is driven across any obstacle, with what Ward Perkins aptly calls “ruthless thoroughness,” whenever there is no reasonable alternative. One might almost think that the new road was built deliberately to impress; in any case the massive viaducts and lofty bridges served to symbolize to the Faliscan peasantry the Roman conqueror’s energy and resources, by which it was hopelessly outclassed. With the same ruthlessness with which they imposed their roads upon the landscape, the Romans imposed law and order upon the countryside. The archaeologicalevidence is the way in which the peasants shifted from their old anarchical life in small strongholds of armed retainers, which is what Grotta Porciosa must have been, down into settled life in Roman cities, or in the open country beside the Roman roads. The great primeval Ciminian Forest, northwest of Nepi, once the fearsome haunt of brigands, was cleared under the Romans and turned into farms. When after eight centuries Roman power waned, the countryside reverted to pre-Roman conditions; the country-folk crept back into the cliff-top villages, there to remain until quite recent times.

These, the results of careful and enjoyable outdoor work in the Italian countryside by a United Nations of archaeologists, enable us to appreciate how the competence of the Roman road-builders made possible both the cold-bloodedness of the Roman conquest and the security of the Roman peace.

*****

That security brought in its train prosperity, and even luxury, of which the symbol is the grandiose Roman public baths. Though Agrippa, Nero, Titus, and Trajan all built baths whose sites and plans are known, the most grandiose, and the clearest in plan, are the Baths of Caracalla, begun inA.D.211. The Baths of Diocletian, built a century later, are equally vast, but their plan has been obscured by the incorporation into their fabric of the church of S. Maria degli Angeli and the Terme Museum. The Baths of Caracalla, known to thousands of visitors as the summer setting for Rome’s outdoor opera, were built on a vast platform, twenty feet high, with an area of 270,000 square feet, greater than that of London’s Houses of Parliament. Excavations in 1938, when the Baths were being prepared for their metamorphosis into an outdoor opera house, revealed in the substructure vaulted service corridors, wide enough for vehicles, widening out at intersections into regular undergroundpublic squares, with provisions for rotary traffic. Access to the lower reaches was by stairs let into the central piers of the main building. The principal entrance to the baths was to the north (over the edge of the platform at the top center of the air-photograph,Fig. 12.4). It was flanked by numerous small rooms which in the difficult post-war years housed teeming families of Italy’s homeless. (Their unique opportunity of a summer evening to admire the sleek prosperity of the operagoers recreated the gulf that yawned between haves and have nots in Imperial Rome, and contributed not a little to Italy’s unrest.)

The main bath building was set in the northern half of the great open space provided by the platform, and was surrounded with gardens. Facing these on the perimeter was a variety of halls, for lectures, reading, and exercise. Those on the east and west were contained in curved projections (exedras). A part of the western exedra appears in the lower left corner of the air-photograph. Beneath it in a subterranean vault was discovered in 1911 what was at that time the largest Mithraeum (shrine of the Persian god Mithras) in Rome.ETo the south (lower right on the photograph) was a stadium whose seats were built against the reservoir which supplied the baths: this was fed by a branch from one of the great aqueducts, the Aqua Marcia.

EIn 1958 Dutch archaeologists excavated a larger one under the church of S. Prisca on the Aventine Hill.

The main block of the baths is distinguished for its axial symmetry. The most prominent room was the circularcaldarium, or hot bath (just to the right of center in the photograph). It is between its main piers that the opera stage is set. Behind it the vast rectangular open space (82 × 170 feet) is most logically interpreted as a grand concourse whence the patrons of the baths (as many as 1600 in peak hours) could move unimpeded to the bathing rooms of their choice. This central room was groin-vaulted in coffered concrete, in three great bays supported by eight piers (Fig. 12.5). The rooms around the central rectangle, with their enormously thick walls, were ingeniously arranged as buttresses to resist the thrust of the colossal vaults.

Fig. 12.4Rome, Baths of Caracalla, air view.(Castagnoli,Roma antica, Pl. 35)

Fig. 12.4Rome, Baths of Caracalla, air view.

(Castagnoli,Roma antica, Pl. 35)

Fig. 12.5Rome, baths of Caracalla, great hall, nineteenth century reconstruction.

The large open spaces at the east and west ends of the main block were exercise-grounds. The exedras adjacent to their inner sides were decorated in the early fourth century with the splendidly satiric mosaics of athletes now in the Lateran Museum. With their broken noses, low foreheads, and cauliflower ears, they are the very type of overspecialized brutal brawn which intellectuals in all ages have delighted to ridicule.

The large rectangular area at the rear center was the cold swimming pool, orfrigidarium; perhaps the rooms on either side were dressing rooms. Below the pavement of the baths the excavators discovered tons of L- or T-shaped iron bolted together in the form of a St. Andrew’s cross. The possible inference is that some part of the baths was roofed with iron girders, designed to support bronze plates ingeniously contrived to reflect sunlight onto the bathers below. (The evidence for the bronze plates and the sunroom is not archaeological but literary, and, chiefly because the literary source had little or no idea what he was talking about, has raised apparently insoluble controversy.)

Excavations were going on in the Baths on a langorous summer afternoon in late June of 1901 which the American architect Charles Follen McKim spent there. That afternoon bore fruit soon after, when he was asked to design for the Pennsylvania Railroad a great terminal station in New York. McKim, lover of Rome and founder of the American Academy there, belonged to the school of architects for whom the grand manner, as found in Roman baths, the Pantheon, and the Coliseum, formed the basis of design for works of the first rank. He desired to symbolize in Pennsylvania Station the monumental gateway to a great city, which should at the same time perform efficiently its function of handling large crowds. To a man of his trainingand prejudices, the Baths of Caracalla seemed to fill the bill. He is reported to have assembled on one occasion a huge band of workmen in the Baths in Rome, simply to test the aesthetic effect of huge scale upon crowds passing under the arches. (Crowds there must always have been, in the heyday of the baths, motley, colorful crowds, speaking many tongues; there is easily room for 2500 patrons at a time. We may imagine them bathing, sauntering, making assignations; conversing idly or upon philosophical subjects; thronging the lecture rooms, the library, the picture-gallery; running, jumping, racing, ball-playing, or watching spectator-sports in the stadium at the back.)

The station plan (Fig. 12.6) shows how creatively McKim imitated Roman architecture. The succession of portico, vestibule, arcade, vestibule, staircase, which leads to what before remodelling of 1958 was the climax in the great central concourse, is noble architectural language, beautiful ordering of space, which Hadrian would have understood, and so is the balance in the façade, the alternating rhythms throughout the building of open and closed, big and little, wide and narrow. In the arcade, the repeated rhythms (now spoiled by advertising) emphasize the traditional, and the movement which is the essence of transportation. The great central hall, once a pool of open space, is even larger (340 × 210 feet, and 100 feet high) than the one that inspired it in the Baths; it is longer than the nave of St. Peter’s. In it McKim contrived to preserve simplicity, dignity, and monumentality in spite of mechanical distractions, as when he used the protruding tops of ventilator shafts as pedestals for lamp-standards. The other refinements, too, are in the Roman manner and material. The rich golden stone facing of the great room is travertine imported from Tivoli, here used for the first time in America (and now badly in need of cleaning). The structural steel and glass in the concourse leading to the trains may have been inspired by the girders in the Baths of Caracalla. The statisticsthat record 1140 carloads of pink granite brought from New England to build the half-mile of exterior walls are in the Roman tradition, and so is the vast extent of the eight-acre structure, and the six years it took to build. The efficiency is Roman, too: access on all four sides, carriage drives twice as wide as the normal New York street of 1910—when the building was opened—a traffic-flow plan that separated incoming and outgoing passengers.

Pennsylvania Station belongs to a vanished era, an era of princely magnificence, of willingness to spend on purely aesthetic pleasure. The young architectural fellows of McKim’s Academy in Rome are impatient with what it stands for, but perhaps they are letting their understandable and proper scorn of soulless copying—of which there is far too much in American monumental architecture—stand in the way of their appreciation of a building which has worn well, and earned accolades—especially by contrast with recent tawdry and misguided additions in plastic—from such emancipated critics, friendly to modern trends in architecture, as Talbot Hamlin and Lewis Mumford. In a day of what a less temperate critic than these has called “the monstrous repetition of cellular facades cloaked with vitreous indifference” by “sedulous apes to the latest expressions of technological baboonery,” it may be salutary to look with understanding at how successful a modern architect of genius can be with a Roman model.

*****

Roman baths needed oceans of water. It was supplied by another triumph of Roman engineering, the system of aqueducts. The eleventh and last of the ancient aqueducts was built by the Emperor Alexander Severus inA.D.226; the earliest, the Aqua Appia, dates back to the same builder and the same year—312B.C.—as theregina viarum. The network (Fig. 12.8) supplied Rome with over 250,000,000 gallons of water every twenty-four hours. When New York was thrice the size of Severan Rome, its aqueducts supplied only 425,000,000 gallons daily.

Fig. 12.6New York, Pennsylvania Station, McKim plan.(A. H. Granger,Charles Follen McKim, p. 77)

Fig. 12.6New York, Pennsylvania Station, McKim plan.

(A. H. Granger,Charles Follen McKim, p. 77)

Fig. 12.7New York, Pennsylvania Station, waiting room, before “modernization.”(Granger,op. cit., fac. p. 82)

Fig. 12.7New York, Pennsylvania Station, waiting room, before “modernization.”

(Granger,op. cit., fac. p. 82)

Fig. 12.8Rome and environs, map showing aqueducts. (V. Scramuzza and P. MacKendrick,The Ancient World, Fig. 33a)

We owe our knowledge of Rome’s aqueducts to three people, one ancient and two modern: Sextus Julius Frontinus, water commissioner under Trajan, whose book on aqueducts survives, Dr. Thomas Ashby, former Director of the British School at Rome, and Miss Esther B. Van Deman of the American Academy. For over thirty years, before modernity removed the traces, this devoted pair tramped the rough country between Tivoli and Rome, plotting the courses of the major aqueducts. Their definitive work is well-nigh as monumental as the aqueducts themselves. Together they explored the mazy course of the aqueduct channels, above ground and below, along crumbling cliffs and the edge of deep gorges, over walls, through briers, across turnip fields, in the cellars of farm-houses and wine-shops. They climbed and waded; Ashby explored downshafts “with the aid of several companions and a climber’s rope,” and when they were through, the courses and the building history especially of Rome’s four major aqueducts, the Anio Vetus (272–269B.C.), the Marcia (144B.C.), the Claudia (A.D.47), and the Anio Novus (A.D.52)—all repeatedly repaired—were better known than they had been since Frontinus’ day, and fellow archaeologists were in a position to draw from their detailed pioneer work important conclusions about Roman hydraulic engineering and about Roman culture.

Following Frontinus’ indications, Ashby and Miss Van Deman found the sources of the four great aqueducts at over 1000 feet above sea level, in springs or lakes in the upper reaches of the Anio valley, near Subiaco, Mandela, and Vicovaro. The airline distance of the sources from Rome varies from twenty-four to twenty-seven miles, but to follow the contours the aqueducts took a circuitous course, so that their actual length is from forty-three to sixty-two miles. Though the modern reader associates Romanaqueducts with the magnificent lines of arches (Fig. 12.9) stretching across a once-empty Campagna near Rome, the fact is that well under a third of a Roman aqueduct’s course was normally carried on arches: the rest was tunnel or side-hill channel. The reason for this was in part economy, in part strategic considerations: an aqueduct below ground is harder for an enemy to find and cut. When the Goths finally did cut the aqueducts in the sixth centuryA.D., the seven hills of Rome became, and remained for centuries, unfit for civilized habitation.

Fig. 12.9Aqueducts near Capannelle, reconstruction (painting).(Deutsches Museum, Munich)

Fig. 12.9Aqueducts near Capannelle, reconstruction (painting).

(Deutsches Museum, Munich)

The four aqueducts, Ashby and Miss Van Deman found, followed the course of the Anio fairly closely from their source to just below Tivoli, where, having lost half their altitude, they turned south along the shoulder of the hills to Gallicano. In this stretch, at Ponte Lupo, the Aqua Marcia crosses a gorge on a bridge that would test the mettle of the most seasoned archaeologist, for it epitomizes Roman constructional history in stone and concrete foralmost nine centuries. After Gallicano the intrepid pair traced the aqueducts’ course westward, where, by a system of tunnels, inverted siphons (the Romans knew that water would rise to its own level), and side-hill channels they cross the broken gorges of the Campagna to a point south of Capannelle racetrack, six miles from Rome, whence they proceed on the famous arches to the Porta Maggiore. From reservoirs in the city the water was distributed in lead pipes (one, of Hadrianic date, has walls three inches thick, and weighs eighty-eight pounds per running foot), with a strict priority, first to public basins and fountains (the Aqua Julia alone supplied 1200 of these), next to baths (extensions of the Marcia supplied those of both Caracalla and Diocletian), then to private houses. Surplus was used for flushing the sewers. Attempts were made to control the priorities by running the pipes for private use only from the highest levels of the reservoirs, but Frontinus complains bitterly of illegal tapping.

In the Gallicano-Capannelle stretch special archaeological ingenuity is required, first to find the channels, and then to decide which belongs to which aqueduct. Where the channels have entirely disappeared, through the disintegrating action of floods, earthquake, tree roots, or plowing, the course can be defined by plotting the occurrence of heaps of calcium carbonate on the ground. This is the aqueduct deposit. Roman water is extremely hard, and the heaps mark where once there were downshafts (putei) for inspection and cleaning the channels, which without such maintenance would soon have become completely blocked with deposit. Frontinus says the downshafts occurred regularly every 240 feet, and Dr. Ashby found many at just this interval.

For distinguishing one aqueduct from another there are many criteria. The first is construction materials. The earliest aqueducts are built of cut stone, the latest of brick. Miss Van Deman was famous for her precise dating of buildingmaterials; she was the only archaeologist in Rome who could date a brick by thetasteof the mortar. A second criterion is quality of workmanship. The Claudia, for example, is notoriously jerry-built: where abutments are found which should be solid, but are instead one block thick, filled in with earth behind, that channel belongs to the Aqua Claudia. A third criterion is mineral deposits. Thus the Marcia was famous for its purity; the crystalline lime deposits were quarried in the Middle Ages, polished, and used to decorate altars. The Anio Novus, on the other hand, is distinguished by a singularly foul deposit. A fourth criterion is directness of course: the older the aqueduct the more sinuously it runs; a channel found meandering by itself along the contours is likely to be that of the Anio Vetus.

The total impression the aqueducts give is one of efficiency, organization, and heedlessness of expense, under the Republic as well as under the Empire. They were built with the spoils of wars or the tribute of provinces. The Marcia, built with the proceeds of the loot of Carthage and Corinth, cost 180,000,000 sesterces, or $9,000,000 uninflated. The Tepula, of 125B.C., was perhaps built with the profits from the organization of the new province of Asia. From Agrippa’s time onward, and especially in Frontinus’ administration, the aqueduct service employed a large bureaucracy; overseers, reservoir-superintendents, inspectors, stonemasons, plasterers (the stone-built channels were lined with two or three coats of hydraulic cement), and unskilled laborers. Maintenance was a constant problem. Arches needed propping, filling in, or brick facing; piers needed to be buttressed or brick-encased. There was no attempt to produce high pressure: lead pipes would not have stood it, and for public use it was not necessary. There was no attempt to make the aqueducts financially self-supporting: their original building was one of the benefactions expected of successful commanders. Since these nabobs expected aquid pro quoin the gift of power, the aqueducts are asymbol, under the Republic of irresponsible oligarchy, and under the Empire of increasingly irresponsible autocracy, though “good” Emperors like Augustus, Claudius, Trajan, and Hadrian had a hand in them. In Augustus’ reign were built the Julia, the Virgo, and the Alsietina. Trajan built a northern line from Lago di Bracciano to Rome’s Trastevere quarter on the right bank of the Tiber: part of its course runs under the courtyard of the American Academy. Hadrian executed major repairs, datable by the omnipresent brick stamps. But even good Emperors knew no way of financing such public works except bleeding the taxpayer. In municipalities, private capital was absorbed in such public enterprise, with no return in income or local employment commensurate with the capital involved. So one major conclusion from Ashby’s and Miss Van Deman’s work is that the Romans were better engineers than they were economists. Let the last word on aqueducts be Pliny the Elder’s: “If one takes careful account of the abundant supply of water for public purposes, for baths, pools, channels, houses, gardens, suburban villas; the length of the aqueducts’ courses—arches reared, mountains tunnelled, valleys crossed on the level—he will confess that there has never been a greater marvel in the whole world.”

*****

One of the latest pieces of Roman engineering, to a knowledge of which archaeology has recently contributed, is Aurelian’s Wall. It has been meticulously studied by a pupil of Ashby’s, I. A. Richmond, now Professor of Archaeology of the Roman Empire at Oxford. Two-thirds of it is still standing (Fig. 12.10), to the disgust of those interested in the unimpeded flow of Rome’s traffic, to the delight of those in love with Rome’s past. It was twelve miles long, twelve feet thick, sixty feet high; it had 381 towers, each with a latrine, and eighteen portcullised gates, nine of which survive (Fig. 12.11). Though the Renaissance humanistPoggio Bracciolini had examined the wall as early as 1431, and the Frenchman Nicholas Audebert had studied it scientifically in 1574, Richmond was still able to make important contributions. He emphasizes, for example, that one-sixth of the wall incorporated buildings: tombs, houses, park walls, aqueducts, cisterns, porticoes, an amphitheater, a fortress. The inference is that the wall had to be built with speed and economy, in the face of the threat of barbarians in north Italy and a depleted treasury. Strategic reasons, of course, dictated the protection of the aqueducts. The use of tombstones as latrine covers shows, says Richmond, that the wall builders “had their religious scruples under excellent control.” It was a sense of urgency and not solicitude for works of art that prompted them, when they built a garden wall at Porta San Lorenzo into the circuit, to leave the statues in their niches and pack them round with clay.

Fig. 12.10Rome, Aurelian’s Wall, from south, near Porta Appia.(H. Kähler,Rom und seine Welt, Pl. 252)

Fig. 12.10Rome, Aurelian’s Wall, from south, near Porta Appia.

(H. Kähler,Rom und seine Welt, Pl. 252)

Aurelian’s Wall and Major MonumentsLEGENDRoads and GatesI Porta Pinciana—Via SalariaII Porta SalariaIII Porta and Via NomentanaIV Porta and Via TiburtinaV Porta Praenestina (Maggiore): major aqueduct junction; Via PraenestinaVI Porta Asinaria—Via TusculanaVII Porta and Via LatinaVIII Porta and Via AppiaIX Porta and Via OstiensisX Porta and Via PortuensisXI Porta Aureliana (S. Pancrazio); Aquae Alsietina and Traiana; Via AureliaXII Porta and Via FlaminiaMonuments1 Forum2 Argentina Temples3 Cloaca Maxima4 Pompey’s Theater and Portico5 Imperial Fora6 Altar of Peace7 Augustus’ Mausoleum8 Subterranean Basilica9 Golden House10 Coliseum11 Cancelleria Palace12 Domitian’s Stadium13 Temple of Venus and Rome14 Pantheon15 Hadrian’s Mausoleum16 Baths of Caracalla17 Baths of Diocletian18 Cemetery under St. Peter’sFig. 12.11Rome, Aurelian’s Wall, plan, with major Imperial monuments.

Aurelian’s Wall and Major Monuments

LEGENDRoads and GatesI Porta Pinciana—Via SalariaII Porta SalariaIII Porta and Via NomentanaIV Porta and Via TiburtinaV Porta Praenestina (Maggiore): major aqueduct junction; Via PraenestinaVI Porta Asinaria—Via TusculanaVII Porta and Via LatinaVIII Porta and Via AppiaIX Porta and Via OstiensisX Porta and Via PortuensisXI Porta Aureliana (S. Pancrazio); Aquae Alsietina and Traiana; Via AureliaXII Porta and Via FlaminiaMonuments1 Forum2 Argentina Temples3 Cloaca Maxima4 Pompey’s Theater and Portico5 Imperial Fora6 Altar of Peace7 Augustus’ Mausoleum8 Subterranean Basilica9 Golden House10 Coliseum11 Cancelleria Palace12 Domitian’s Stadium13 Temple of Venus and Rome14 Pantheon15 Hadrian’s Mausoleum16 Baths of Caracalla17 Baths of Diocletian18 Cemetery under St. Peter’s

Fig. 12.11Rome, Aurelian’s Wall, plan, with major Imperial monuments.

Richmond also found that in the phase of the wall identified as Aurelian’s by building materials and brick stamps, the workmanship differed sharply from one curtain to another. The inference from this was that various stretches were assigned to various gangs of workmen—mostly civilian, since the legions were needed in the North, and for Aurelian’s campaign against the Parthians in the East. These workmen belonged to the various city guilds, orcollegia, some experienced in construction, some not, but all pressed into service in the emergency.

Richmond distinguished the bottom twenty-four feet of the wall as the original phase. It was built of brick-faced concrete—that its bricks were often second-hand is inferred from the many Hadrianic stamps—surmounted by a gallery with loopholes outside and an open, bayed arcade inside, with a crenellated wall-walk above. Access to the wall was by the towers only; Richmond inferred that the planner aimed to keep excited and irresponsible civilians from interfering with defense, and the wall-detail from pilfering or philandering in the adjoining houses and gardens. In this phase the wall was plain, efficient, functional, simple, and uniform, built to a standard size and pattern. Its many gates show that there was no very formidable danger: the intent was to provide a barrier to shut chance bodies of undesirables out of the city as on far-flung frontiers structures like Hadrian’s Wall shut them out of the Empire.

In its second phase another thirty-six feet of wall was fitted on to the base provided by Aurelian’s. In some places the addition was only six feet thick, the other half of the original width being left as a passage for the circulation of materials and messages. A wall sixty feet high reduced the required number of defenders, since it had nothing to fear from an enemy equipped with scaling ladders. In this phase machines did the work of men: if there were twoballistaeto a tower, the expensive and impressive total of pieces of artillery would have been 762. Heightening the wall meant heightening the tower, sometimes to five stories. A start was made toward monumentalizing the gateways, but it peteredout, though the effect can be admired in the Porta Asinaria near the Lateran, which was restored in 1957–58. For the workmanship of this phase is identical with and therefore of the same date as the Basilica and Circus of Maxentius (who reignedA.D.306–312); when he was defeated by Constantine at the battle of the Milvian Bridge, and the capital moved to Constantinople, neither the money nor the motive for monumentality any longer existed.

The next major alteration is dated by inscriptions toA.D.401–403, the reign of Honorius. It was prompted by the threat that the city might be sacked by Alaric the Visigoth. It involved second-hand stone facing for the curtains of the wall, and square bases for the towers. The photograph (Fig. 12.10) shows this Honorian phase at the Porta Appia. The upper stories of the round towers belong to Maxentius’ addition, while halfway up the face of the curtain between the rectangular towers to the left of the gate can be seen the patching required to add Maxentius’ brickwork to the battlements of Aurelian’s original wall. (To distinguish the building phases of the Porta Appia, Richmond had to crawl into the base of a tower through a very small hole, while a small uninvited audience bet on his chances of sticking.) The new battlements were built in a way that shows that in this phase Rome could no longer afford artillery: archers replacedballistae. By now the Empire is Christian, and crosses begin to appear on the keystones of the gate arches, as prophylaxis against the devil. Later, in what Richmond describes as “an age of vanishing standards of faith and hygiene,” an indulgence of 100 days was granted for kissing one of these crosses. They were no help: the wall was assaulted by earthquakes (A.D.442), and by Goths (A.D.536 and 546), and repeatedly repaired. Belisarius in 547 restored it all, with the help of palisades, in twenty days, and equipped it with spring-guns the force of whose projectiles could impale five men, and with mantraps or deadfalls, barrow-like devices which could be pushed over onassailants. But the repairs are botched work, appropriate to what Rome had become: no longer an Imperial capital, but a minor metropolis of an outlying Byzantine province. All the same, the wall was never really breached till the advent of heavy artillery, when Garibaldi’s men attacked the Porta San Pancrazio in 1849.

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