Ancient History & Civilisation

Chapter Six

Between the Aqua Virgo and the Tiber: Water and the Field of Mars

To Vergil, it was the majestic “Father Tiber”; to Statius, the “prince of rivers”; to Dionysius Periegetes, the “most kingly of rivers”; and to Martial, the “sacred Tiber.”1 Encapsulating these ancient assessments, a recent study describes the Tiber as the “center of traditional stories of the foundation of Rome in which it appeared as a benevolent collaborator.”2 The great river carried the basket bearing the twins Romulus and Remus as well as the sacred grain of Tarquinius Superbus that formed the Tiber Island.3 For Romans it was both source and receptacle of divine power. In Vergil's Aeneid, the river's associated god Tiberinus appeared to Aeneas and prophesized the future site of Rome along the river's banks.4 Sacred springs such as the Cati fons drained into the Tiber (by way of the Petronia Amnis and other rivulets), and Ovid wrote that nymphs and naiads haunted the river's shoreline.5

Occasionally, the Tiber overflowed its banks, and while Plutarch wrote that citizens regarded one of its highest floods, which occurred during the brief reign of Otho, as a “baleful sign,” this was not always so.6 Interpreting the Tiber's floodwaters in 27 a positive omen, soothsayers prophesized that Augustus would “hold the whole city under his sway.”7 For much of the year, however, the river remained safely contained within its banks. Pliny the Elder described the Tiber as the “tranquillest purveyor of the produce of the whole globe.”8 Livy wrote that it carried on its placid surface the “fruit of inland places” and the “seaborne produce from abroad,” and as Juvenal recorded, the river brought the languages and customs of distant countries to the capital.9 In places the current flowed calmly enough to allow swimming. Cato the Elder taught his son to swim in the Tiber, and soldiers would take a dip following military exercises.10 Generally praised in the ancient sources, the Tiber nevertheless had its more dangerous side.The Tiber's heavy winter flows not only led to the often destructive flooding of low-lying areas of the city but also likely contributed to the presence in the late summer and fall of “tertian fever,” a malady known today as malaria. The river further served as the depository for the refuse of sewers, baths, and distant streams connected to the city by aqueducts.11 As Nicholas Purcell has aptly summarized, the Tiber was to Romans “their blessing and their curse, ambiguous from mouth to source.”12 Nowhere in the city was this truer than in the Campus Martius, whose long, winding western border was etched by the Tiber's flow.

Water from the West

From the embankment by the Mausoleum of Augustus to the Pons Fabricius behind the remains of the Theater of Marcellus, the river wends its way south then west and then south again for 2.9 kilometers, 1.5 kilometers longer than the path between parallel points along the very straight Corso, the modern Via Flaminia. The Tiber, therefore, constituted a lengthier border to the Field of Mars than the eastern boundary. This extended border was occasionally a dangerous one. Runoff from more than 15,000 square kilometers of Italian hills drains into the Tiber, and during the winter and spring rains, its waters swell. Before the construction of the late nineteenth-century floodwall, the Tiber would occasionally overflow its banks when it reached the city. Ancient Rome was located precisely where the river's floods reached their maximum level.13 When the torrent coursed through the channel toward the plain north of Rome, the Campus Martius was among the first areas to suffer the effects of relentlessly rising water.14 As a low-lying marsh, the Field of Mars was only about three to five meters above the Tiber's normal level.15 Accordingly, a “minor” flood surrounded all of the central Campus Martius monuments, including the Theater of Pompey, the Theater of Balbus, the Saepta Julia, the Pantheon, and the Largo Argentina temples, while a “major” inundation reached all the way to the Via Flaminia, covering all of the Campus Martius.16

How often the Tiber overflowed its banks is a matter of debate, because ancient records are, at best, anecdotal and spotty. Only fifteen floods are recorded in Rome in the four centuries preceding the reign of Augustus, although six more are noted just in the four-decade rule of Rome's first emperor.17 On the basis of modern data and the best-documented ancient sources, however, Gregory Aldrete argues that flooding in Rome occurred to a height of thirteen meters above sea level about every four years and to a height of at least fifteen meters above sea level approximately every nineteen years.18 Put another way, Romans could count on much of the Campus Martius submerged under three meters of water twice a decade. According to Livy, there were two great floods in the year 215 B.C.E.; in 189 B.C.E. alone, the Tiber flooded the Campus Martius twelve times.19 The duration of the inundations obviously varied. Cassius Dio reports that the floods of 27 and 23 B.C.E. each made the city navigable by boat for three days, while the flood of 5C.E.allowed boat passage for an entire week.20

The ancient descriptions of Tiber overflows paint a scene of devastation in the low-lying areas of the city. In the flood of 241 B.C.E., several unidentified buildings were knocked down by the torrential force of the floodwaters or collapsed because of waterlogged, destabilized foundations.21 A flood in 69 B.C.E. caused disruption of the grain supply and subsequent starvation, and the force of the floodwater itself could be lethal: “Many were swept away in the public streets, a larger number cut off in shops and in their beds.”22 Pliny the Younger described vividly the loss of property from floods: “Those who live in highlands out of the reach of these terrible storms have witnessed, here, the household paraphernalia and weighty furniture of the wealthy, there, the simple tools of the farm, over there, oxen, plows, and the plowmen themselves, here, herds set free and straying, jumbled among the trunks of trees, or the beams and roofs from villas, and all of it floating about randomly and widely.”23

The problem of flooding in Rome was not unique to the northern plain. Streams ran through the valleys that separated the hills of the city, eventually draining into the Tiber. The Petronia Amnis discussed in Chapter 1 flowed from a spring on the western side of the Quirinal Hill and then cut a course through the widening northern plain before reaching the river north of Tiber Island (Plan 1).24 Springs and streams also burbled through the lower ground of the Roman Forum as well as through the valley between the Palatine and the Aventine where the Circus Maximus was constructed. The lowlands were composed of impermeable clays that held water near the surface, leading to swamplike conditions.25 Livy notes that Rome's early settlers found only “forests and marshes.”26The Circus Maximus area would flood when the Tiber was about five to seven meters above normal, and the fora would suffer inundation when the river was ten to twelve meters above normal.27 Floodwaters in 12 C.E. were high enough to disruptgames in the Circus Maximus, which were temporarily transferred to the still-dry area of the Forum of Augustus immediately north of the Roman Forum.28 Indeed, all of the city's flatland between the hills was continually in peril of flooding from a major rise of water cresting the Tiber's banks. In 241 B.C.E., nearly all the low-lying areas of the city were submerged, and again in 189 B.C.E., including the plain of the Campus Martius.29 In 27 B.C.E., the Tiber “overflowed and covered all of Rome that was on low ground, so that it was navigable for boats,” and in 15 C.E. floodwater “flooded the lower levels of the city.”30

The few anecdotal reports of floods from ancient writers that can be tied to precise dates do not provide a clear pattern of flood stage seasonality. Ovid notes that the infants Romulus and Remus came to rest downstream during the winter floods, and theEquirria held in March occasionally relocated to the Caelian Hill because of flooding in the Campus Martius.31 A flood in 13 B.C.E. occurred on July 4 at the time when Augustus returned to Rome from his western campaigns.32 The flood of 12 C.E. that forced the move ofgames from the Circus Maximus to the Forum of Augustus occurred around May 12.33 More accurate records of water levels and flooding during the past several centuries support the view that most floods of the Tiber in ancient times occurred from the late winter to the early spring.34

To add to the misery of a swampy, occasionally flooded environment were the pests that lived in such places, especially mosquitoes, and the disease they carried – malaria. Romans were all too familiar with the problems of mosquitoes in marshy environments.Columella, a first-century C.E. writer on agriculture, advised that buildings should not be too close to a marsh “because it throws up an evil odor during the summer heat and produces insects armed with dangerous stings, which swoop upon us in dense swarms.”35Romans did not completely understand the connection between mosquitoes and malaria, but they did know that swamps contributed to deadly spikes in body temperatures.36 Writing in the first century B.C.E., Varro noted that “care must also be taken in marshy areas…because certain small animals breed there. These animals cannot be seen with the naked eye and enter the body through the mouth and nostrils in the air and cause severe disease.”37 Nineteenth-century epidemiological studies in Rome provide some indication that floods contributed to populations of malarial mosquitoes that peak in mid- to late summer, making August the month of greatest risk for contracting the disease.38 The poet Juvenal suggested that malaria took its greatest toll in the fall.39

Despite the inundations that washed over the Campus Martius in the late fall to early spring months and the disease-bearing mosquitoes that infested the plain in the late summer, the Romans persevered, turning the Field of Mars into a monumental complex of temples, colonnades, theaters, baths, and stadiums. Why did they remain so steadfast? One answer is the Roman attitude toward natural events combined with the practical needs of an expanding city and improving engineering and construction skills.40 Romans viewed the Campus Martius as both sacred and economically valuable real estate; disease and flooding could be mitigated or, in the very least, accommodated by all manner of construction projects. The historical, religious, and practical importance of the northern plain ensured that the Field of Mars would not be left undeveloped. Moreover, the slow, incremental development of the Campus Martius over several centuries allowed for necessary modifications to infrastructure by greater use of stone and water-resistant mortar that could withstand the challenges of an alluvial environment. Certainly, in the worst situations, the plain could be temporarily abandoned because the low-lying region was within a fast walk of hilltop retreats from which the devastation below could be witnessed.41 People whose lives were lost in floods were, according to Cassius Dio, those “who did not take refuge in time on the highest points.”42 The hills of Rome also provided some protection from mosquitoes in the summer.43 According toCicero, “The site that Romulus chose…was a healthful spot in a plague-ridden region: the hills not only receive a breeze, but they bring shade to the valleys.”44

When the Campus Martius was simply a military mustering ground and voting precinct, the conditions presented by the wetland soil and seasonal flooding were relatively easy to avoid. Armies vacated the area in the spring following the worst months for floods and ahead of the arrival of mosquitoes. They returned in the fall in advance of the winter rains that swelled the Tiber and after the summer swarms of insects diminished. Moreover, in addition to the attractiveness of the open space of the Field of Mars for military maneuvers, the Tiber provided the area particular benefits. Vegetius, a fourth-century C.E. writer on military science, while discussing the importance of soldiers learning to swim, noted, “The ancient Romans…chose the Field of Mars as the most commodious for their exercises on account of its vicinity to the Tiber, that the youth might therein wash off the sweat and dust, and refresh themselves after their fatigues by swimming. The cavalry also as well as the infantry, and even the horses and the servants of the army should be accustomed to this exercise, as they are all equally liable to the same accidents.”45

Horse racing and religious celebrations that were hosted in the Campus Martius in the spring and fall also fell outside the most dangerous months, although, as noted previously, the Equirria was accommodated elsewhere when the racetrack was flooded. The situation changed, however, when permanent structures began to rise in the Field of Mars. Drainage now needed to be considered. The Romans had extensive experience with removing water. Since the time of Rome's last king, Tarquinius Superbus, Rome's largestdrainage conduit, the Cloaca Maxima, channeled water to the Tiber from the valley between the Quirinal and the Esquiline, an area that included the Roman Forum.46 As its qualifier maxima implies, the sewer line was huge: large enough to fit a hay wagon. When later improved by Agrippa, the cloaca was navigable by boat.47

Similar networks of pipes and ditches would have been necessary to remove standing water from the Campus Martius. Evidence indicates that there were, in fact, significant sluice lines through the Field of Mars, although nothing as massive as the CloacaMaxima. Certainly some surface water and runoff was captured by the Petronia Amnis, which later joined with another channel as part of the reworking of Rome's sewer system by Agrippa.48 Ancient lines have been discovered in the area of the Pantheonand the Baths of Agrippa, as well as in the southern Campus Martius, indicating that the Romans made significant efforts to remove the surface water that accumulated in the Field of Mars.49 Given the fact that Agrippa's Pantheon was built in the lowest part of the Campus Martius, some drainage must have been installed in its vicinity by the time of its construction in 27 B.C.E.50 Vitruvius recognized that quadriporticoes were often built in low-lying regions and provided directions for draining the space inside of the colonnades.51

Beginning in the early imperial era, surface water may have also collected in the Stagnum Agrippae, a large artificial lake fed primarily from the Aqua Virgo's waters that passed through the Baths of Agrippa built just to the east.52 The Stagnum itself drained to an artificial canal that ran for about 800 meters before emptying into the Tiber somewhere between the modern Ponte Vittorio Emanuele and Ponte Sant’Angelo (Plan 3, No. 29).53 Called today the Euripus Thermarum Agrippae, the concrete channel was less than 2 meters deep and possibly followed the route of a stream that drained the marshy Caprae Palus. A section of the channel is still visible beneath the Palazzo della Cancelleria.54

Although the drainage system did not prevent flooding, it did at least allow construction on marshy soil. Cattails and other marsh grasses gave way to large stone buildings, colonnades, and paving blocks. Ironically, covering the marshes with an impervious stone surface aggravated the effects of floodwater rising in narrow streets.55 During flooding, the drainage to the Tiber would back up, speeding the rise of water in the Campus Martius.56 Pliny the Younger noted with respect to a flood during the reign of Trajan, “Although drained by a spillway made by the foresight of the emperor, the river covers the valleys, swims into the fields and entirely covers over the flat ground.”57

Although the Romans had the technology to contain the Tiber's floodwaters through use of a floodwall, there is no evidence that they attempted to do so.58 That effort would not begin in earnest for 1,900 years. One early plan to redirect the Tiber was likely intended to increase land for Rome's growing population rather than for flood control and might not have provided protection from flooding in any event. Cicero wrote that Julius Caesar had a grandiose plan to divert the Tiber north of the Milvian Bridge and channel it over 1.6 kilometers through an artificial drainage line west of the Vatican Hill.59 The plan was never implemented, of course, and it might have been opposed on both religious and practical grounds had a serious effort been put forth.60 The ancient citizens of Rome did, however, undertake solutions to the flooding problem. Suetonius reported that Augustus attempted to solve the problem by dredging the river's rubble-filled bed. Obviously, the effort failed over the long term. The city's low-lying areas, including the Campus Martius, continued to flood.61 Tiberius set up a commission of five members to regulate the Tiber in an effort to eliminate both winter floods and summer droughts. Despite this measure and later attempts to control the river, there is no record that imperial engineers successfully deployed any means of reversing the river's natural proclivities.62

Though failing to stop the floods, the Romans undertook various construction techniques that mitigated the impact of inundations in the Campus Martius. First and foremost, they erected massive brick and mortar as well as stone buildings that could withstand the effects of rising water. For instance, Hadrian's Pantheon, located in the lowest area of the Campus Martius (the former Caprae Palus), was constructed with a drum of brick-faced concrete 6.2 meters thick.63 The concrete foundation walls of Pompey'stheater, also on the edge of this same depression, were 1.5 meters thick, faced in quasi reticulate on top of large blocks of tufa.64 While the ancient writers describe the devastation of structures in the Campus Martius resulting from a series of fires, there is no similar evidence that the major monuments in the Field of Mars suffered significantly from the Tiber's overflow.

Although soaking floodwaters could degrade the walls and foundations of wooden buildings or those built with poor-quality brick and concrete, the public baths, temples, and permanent theaters of the Campus Martius were sufficiently impermeable to water, and thus maintained their structural integrity.65 In addition, some buildings remained dry on the interior because they were raised on bases above the flood level. For instance, the temples in the Forum Holitorium close to the Tiber's edge and the nearby Temple of Apollo Sosianus perched on podia approximately fifteen meters above sea level, or above all but the worst inundations in the Campus Martius.66 A building type that did suffer heavily during Rome's floods was the apartment complex (insula). Often of shoddy construction, the foundations of these structures could be jeopardized after several days of soaking in floodwater.67 Tacitus wrote that in the flood of 69 C.E., “Apartment houses had their foundations undermined by the standing water and then collapsed when the flood withdrew.”68 During the fourth century C.E., there were numerous insulae in the Campus Martius, and while there are no extant descriptions of flood damage to apartments in the Field of Mars per se, they must have been as prone to destruction as those located in other parts of the floodplain.69

Rising ground levels due to constructions in the Campus Martius would have mitigated the impact of floodwaters, but as we know from the numerous floods in the area until the construction of the floodwall that follows both banks of the river, it certainly did not thwart the Tiber's seasonal inundations. The Pantheon of Hadrian, for instance, was built on a foundation approximately 2.5 meters higher than the original temple constructed by Agrippa.70 Much of the northern plain was raised approximately 1.2 and 2.4 meters between the reigns of Vespasian and Hadrian.71 In addition to the natural accretion, this artificial fill has caused the ground level of the Field of Mars to rise to the point that most of the extant ancient monuments have their foundations several meters below modern street level. The base of the Temple of the Divine Hadrian is 5 meters beneath the pavement (Figure 29) and the street elevation behind the Pantheon has risen 10 meters.72 The Flavian pavement in which the horologium meridian is set rests 6.25 meters below street level.73 The combination of a floodwall and raised ground level has resulted in the significant reduction of floods that challenge the Campus Martius, but not their elimination.74 Permanent reminders of the height of floods and of the Tiber's alluvial impact over the past several centuries can be found on incised stone markers throughout the area.75

Water from the East

On June 9, 19 B.C.E., clear, cold water rose from the soil beneath an estate formerly owned by one of Rome's great generals and politicians, Lucius Licinius Lucullus. Located near the eighth milestone east of the city limits, the spring was thought by some ancient writers to have been revealed by a young maiden to soldiers who were searching for water. In her honor, it was called the “Virgo,” the Virgin.76 With construction overseen by Agrippa for the final two years of work, the Aqua Virgo sent its waters on a lengthy and circuitous journey to the heart of the Campus Martius.77 By coincidence or otherwise, June 9 was the feast day of Vesta, the goddess of the Vestal Virgins, and just as the flame on the hearth of the Vestales was to be eternal, the Virgin's water bubbling from the spring and flowing toward Rome on that early summer day has, in fact, never ceased. The water first entered a catch basin from the various underground springs with just under one cubic meter of water pouring forth every second into the Virgo's channel (specus).78From there, it flowed through an underground conduit that had been built along a nearby road, now the Via Collatina, and traveled west down a slight slope toward the city.

Near the later-built Porta Maggiore, the water was channeled north and then west again under the Pincian Hill, crossing under another of Lucullus's properties, his famous gardens, the Horti Luculliani.79 Curving south, the flow of water continued through thespecus down the hill near the modern Spanish Steps. There the conduit emerged and was carried over 139 stone arches for approximately one kilometer through the city.80 It traveled first south about 536 meters to its modern terminus, the site of the famous TreviFountain built seventeen centuries later. A relief panel on the fountain commemorates Agrippa's construction project (Figure 30). From the area of the Trevi the water wended west across the Via Flaminia, and at last arrived in the central Campus Martius.81Just east of the Pantheon and north of the Saepta Julia, the water poured into a distribution chamber (castellum), before leaving in different directions through lead pipes (fistulae) to meet the needs of the rapidly developing Field of Mars.82 Entering Rome at only 20 meters above sea level, the Aqua Virgo was one of the lowest aqueducts, but then its waters were heading to one of the lowest parts of the city.83

29. Detail, Temple of Divine Hadrian, Piazza di Pietra, Rome. (Photo: Paul Jacobs)

30. Agrippa supervising the Aqua Virgo construction, Trevi Fountain, Rome (eighteenth century). (Photo: Paul Jacobs)

On this June morning in the early imperial era, most of the Aqua Virgo's supply traveled a short distance from the castellum before splashing into the empty pools that had been built into a large bathhouse just south of the Pantheon. Begun under the direction of Marcus Agrippa just six years earlier as a dry sweat bath, the Thermae Agrippae could now offer visitors to the Campus Martius a full bathing experience.84 From the bathhouse area the water ran directly west to the Stagnum Agrippae that, in turn, drained into the Euripus Thermarum Agrippae.85 The Virgo also poured as much as nineteen cubic meters that first day, one-fifth of the total flow that reached the city, into another euripus, the newly constructed Euripus Virginis, a channel that, according to the first-centuryC.E.Roman water commissioner Sextus Julius Frontinus, derived its name from the source of the water pouring through it.86 Unlike the Euripus Thermarum Agrippae, the Euripus Virginis was apparently employed as a recreational swimming facility.87 The termeuripuswas derived from the name for a narrow strait between the island of Euboea and mainland Greece, and as noted by Dyson, “This type of fanciful geographical identification was there especially associated with villa architecture and further emphasized the shift in the Campus Martius from virtus to otium.”88

Within the Euripus Virginis, the Virgo's water flowed west and then south around the Theater of Pompey before reaching the Tiber in the area of a bridge thought to be the Pons Agrippae.89 Whether on that June day or some time later, the Virgo's spring water was carried over the Pons Agrippae, to serve the villas on the Tiber's west bank, the Transtiberim.90 Whatever the extent of the Virgo's ultimate reach on that first day, approximately 74,000 cubic meters of groundwater entered Rome through the aqueduct and, with few interruptions, have been doing so for more than two millennia.91

The Aqua Virgo was designed to provide for the intensive water needs of this section of the city, ultimately filling 90 percent of the Field of Mars's supply.92 According to Frontinus, it was one of three major aqueduct projects initiated by Marcus Agrippa that, in combination, more than doubled the available fresh water for a burgeoning population.93 But while the other two supplied a large part of their bounty to private homes and public basins and troughs, the Virgo's waters, according to Frontinus, went primarily for public works (opera publica), an undefined category that likely included Agrippa's baths, the Stagnum, and the various entertainment venues, as well as their gardens, such as the quadriporticus connected to the Theater of Pompey.94 The Aqua Virgo's supply to public works is impressive, with 60 percent of the water volume consumed by all of the opera publica in the city being furnished by this aqueduct, almost four times the volume of the next highest provider, the Aqua Claudia / Aqua Anio Novus.95 By contrast, Frontinus reported that only 4 percent of the lacus, public basins that provided, among other purposes, domestic drinking water for those without plumbing, was to be found in the Campus Martius.96

As Pliny the Elder makes clear, the aqueducts and the great volumes of water they carried to the city were a source of marvel to ancient Romans. “If we take into careful account the abundant supplies of water in public buildings, baths, pools, conduits, houses, gardens, suburban estates, if we reckon from how far the water comes, the raised arches, the tunneled mountains, the leveled valleys, we shall admit there has never been anything more marvelous in the whole world.”97 According to Suetonius, evenAugustus highlighted the far-reaching benefit of Agrippa's Aqua Virgo, for he records that when people complained about the high price and scarcity of wine, the emperor retorted, “My own son-in-law Agrippa has taken good care, by building several aqueducts, that men shall not go thirsty.”98 As late as the sixth century C.E., the writer Cassiodorus praised the Virgo, long revered for its purity: “Purest and most delightful of all streams glides along the Aqua Virgo, so named because no defilement ever stains it. For while all the others, after heavy rain show some contaminating mixture of earth, this alone by its ever pure stream would cheat us into believing that the sky was always blue above us. Ah! how express these things in words worthy of them?”99

Apart from the significant contribution of the Virgo's waters to the development of the Campus Martius, the monumental structure through which it traveled had a significant visual impact on the space. Following the northern line of the Saepta Julia, the aqueduct separated the development in the central Campus Martius from the relatively open northern portion of the plain. The point at which the arches of the Aqua Virgo crossed the Via Flaminia provided a visual boundary to those traveling to Rome from the north, and this arcaded signpost begged for imperial decoration (Plan 3, No. 4). In 51 or 52 C.E., Claudius rebuilt one of the arches of the Aqua Virgo as it crossed the Via Flaminia, redesigning it as a single triumphal arch celebrating his successes in Britain eight years earlier.100 A dedication to the emperor, believed to be from the arch, is now visible in the Capitoline Museum courtyard.101 This was not the only section of the Aqua Virgo adorned by Claudius. An extant section of the Aqua Virgo northeast of the location of the arch that once crossed the Via Flaminia also displays an honorary inscription to Claudius. The fading but still legible words praise the emperor for restoring the Aqua Virgo after his predecessor Caligula had removed some of its stones for a building project (Figure 31).102

31. Section of the Aqua Virgo with Claudian inscription, Via del Nazareno, Rome. (Photo: Paul Jacobs)

Before the construction of the Aqua Virgo, water-related spectacles were held in the Campus Martius near the Tiber's edge. The aqueduct's construction made them possible in numerous venues. Three decades before the Virgo was built, Julius Caesar ordered the creation of a shell-shaped lake near the Tiber, likely connected to the river by a channel, in honor of his triumph of 46 B.C.E., using it to reenact naval battles between the Egyptian and Tyrian fleets.103 Suetonius tells us that for this event “a large force of fighting men” manned ships that had as many as four levels of oarsmen. Because these vessels did not sit low in the water, the basin may only have been about one and a half meters deep.104 The basin was left in place for approximately three years.105 Obviously, the Virgo made such aquatic events possible farther from the Tiber's edge. Augustus flooded the Circus Flaminius in 2 B.C.E. to display thirty-six crocodiles.106 Caligula filled the Saepta Julia with water in order to display a single ship, and because of its location by the castellum of the Virgo, the Saepta undoubtedly was fed by that source.107 Nero held a naumachia in his wooden amphitheater, complete with fish and other sea life, and reenacted the Battle of Salamis.108 If his structure was located northwest of the Pantheon,the Aqua Virgo likely supplied the water on which the ships floated.109

With the addition of the Aqua Virgo's spring water, Agrippa also turned the low-lying Goat Marsh into a well-manicured parkland (Horti Agrippae). Large landholdings of Pompey in the Campus Martius that passed into the hands of Mark Antony and then into those of Agrippa during the turmoil of the Civil War became the site of his building projects.110 Bordered by the Theater of Pompey to the south, the Pantheon and Baths of Agrippa on the east, the later-built Stadium of Domitian on the west, and Baths of Nero on the north, Agrippa's property was turned into a park with the Euripus Virginis and the Stagnum as its most prominent water features.111 The gardens contained the famous Fallen Lion by the sculptor Lysippus, brought to Rome from Greece by Agrippa, and the Stagnum was used on at least one occasion to float a pleasure barge.112 Originally part of Pompey's villa by his theater, the park was, according to Katherine von Stackelberg, transformed by Agrippa “into a showcase for his aquatic achievements” with the water features serving as “a monument to Augustus's admiral, the man who brought water to Rome.”113 Bequeathed in Agrippa's will to the public for its enjoyment, the park provided a relaxing, verdant venue for pedestrians where wild swamp grasses had once grown.114 Nero later introduced exotic birds and wild animals, turning the public area into something of a zoological park.115 Following the Roman penchant for forcing the natural environment to submit to the needs of urban expansion, Agrippa channeled the Virgo's spring to suit his development plans and, in doing so, assisted in the transformation of the swampland into a well-ordered entertainment district.

The greatest role of the aqueduct, however, was to serve as the water source for Rome's first grand public baths, the Thermae Agrippae. Covering more than 8,000 square meters, the baths, in conjunction with the Stagnum, the Euripus Virginis, and Agrippa's gardens to the west, created a complex for swimming, boating, exercise, and strolling. Until the completion of the Thermae Agrippae, Romans would have bathed at one of approximately 170 privately owned bathhouses known as balneae tucked away in small spaces throughout the city.116 How many balneae were in the Campus Martius at the time Agrippa built his baths is unknown, although Cicero refers to one that may have been in the vicinity of the later-built Theater of Balbus.117 Although many private bathhouses were dry sweat baths without hot water plunges, those that had pools may have received their water supplies from the runoff of public troughs.118 Swimming generally took place in the Tiber, although a swimming pool was constructed on the southern side of the city as early as the fourth century B.C.E.119 Agrippa permanently changed the bathing experience for most Romans by creating an indoor-outdoor leisure facility that combined large areas for bathing, gymnastics and games, swimming, social commerce, dining, business negotiations, shopping, and displays of art.120 Where once Romans came to muster or witness military parade formations in a swampy and austere environment or practice their swimming skills in the muddy Tiber, now with an abundant supply of fresh spring water, they bathed and swam in clean pools and promenaded in lush but tamed green spaces surrounded by marble baths, theaters, and manubial temples. Augustus's comrade embellished the baths with decorative stucco, mosaics, encaustic painting, and 300 statues, including the famous Apoxyomenos by Lysippus. When it was removed a few years later by Tiberius to decorate his bedroom on the Palatine, a riot nearly broke out, resulting in its return to the Thermae Agrippae.121

While the baths originally charged a fee to its users, on Agrippa's death in 12 B.C.E., the facility and the adjoining park were given over to the Roman people for their free use.122 Constructed as part of his building program for the central Campus Martius, the Baths of Agrippa was the first bathing complex in Rome to be maintained by the state.123 By bringing water to the center of the Field of Mars, Agrippa helped anchor it as space to be shaped by imperial prerogative but available to a public that was daily reminded of the emperor's largesse.

Given the presence of his large landholdings in the Campus Martius and Agrippa's overall vision for its development, his decision to build a monumental bathhouse in this vicinity is logical. Nevertheless, unlike other nearby building projects with which Agrippa was associated such as the Saepta Julia and the Pantheon, the baths required complicated infrastructure improvements, equipment, and a constant and large supply of water and regular maintenance. Water was already available in other parts of the city where the baths could have been supplied more easily without the need to negotiate with landowners for the right to lay a channel through many kilometers of private property.124 Why, then, add a large bathhouse, exercise space, and swimming facilities to his grouping of structures in the central Campus Martius? A possible answer is found in the fact that the Virgo was important to bringing drinking water to the other side of the Tiber. Baths between the source and the Transtiberim could make good and noticeable use of this bountiful supply, allowing Agrippa to simultaneously accomplish several significant goals.125

A different reason that reflects the sacred past of the space helps further to explain the choice of the Field of Mars for the first imperial bath. At the same time that Agrippa was reorganizing the space of the Campus Martius, he was advising Augustus to reorder society with new institutions, including a sports and paramilitary training program for adolescents of the upper classes designed to create a new generation of military and civic leaders.126 Cassius Dio records Agrippa's recommendations:

With regard, then to the senators and the knights, this is the advice I have to give you, – yes, and this also, that while they are still children they should attend the schools, and when they come out of childhood into youth they should turn their minds to horses and arms, and have paid public teachers in each of these departments. In this way from their very boyhood they will have had both instruction and practice in all that they will themselves be required to do on reaching manhood, and will thus prove more serviceable to you for every undertaking.127

There was probably no more meaningful space to build an exercise facility on a grand scale than in the area where Romulus and Cincinnatus had gathered their troops and Augustus himself had practiced his equestrian exercises as a youth.128

The Baths of Agrippa also would have provided an added attraction to the formal entertainment venues in the area. The Theater of Pompey and its portico-enclosed grounds for ambulations and assemblies were nearly adjacent to the bathhouse. Dedicated shortly after the Virgo began to deliver water to the baths, the theaters built by Cornelius Balbus and by Augustus in honor of his nephew Marcellus were only a few minutes’ walk south. Patrons of Agrippa's baths would not have limited their visits to those days when shows were being performed, however. Attendance at bathhouses was part of a daily ritual of congregation that involved cleansing, exercise, relaxation, and conversation.129 Roman citizens worked from daybreak to noon, had a light lunch and rest, and then went to the baths in the early afternoon for a couple hours when the pools were heated to their ideal temperatures.130 A trip to the theater might follow the bathhouse experience.131 While Agrippa's baths were on the outskirts of the city, and there were numerous small bathhouses elsewhere, for about eight decades, until Nero's imperial baths were constructed close by in the Campus Martius, they were the largest and likely the most prestigious place for Romans to gather for the bathing experience.132 And for most of their history, Agrippa's baths were free of charge. Even after other, larger baths opened, they remained popular. Martial complained wearily that while he preferred the new Baths of Titus located near the Colosseum, his patron Fabianus insisted that the poet accompany him to the then century-old Baths of Agrippa for a late afternoon wash.133

Those partaking of Agrippa's baths for an afternoon of relaxation may have entered through an opening in the west side of the structure near the Stagnum.134 Entering a courtyard with a pool in the center, bathers would have turned left and proceeded into a two-story building used as a changing room (apodyterium). Street clothes were placed in cabinets, on shelves, or left in the safekeeping of personal slaves, and a light garment, possibly of linen, would be donned for exercise. From there exercises could be taken in the courtyard or in front of the changing room. These moderate activities might include handball, running, walking, and boxing, performed with only enough vigor to create a slight sweat.135 With the ringing of a bell to signal the availability of the hot baths, bathers would stop their exercises and head first to the warm bath (tepidarium) located in a room to the left of the changing room.136 Relaxation in the warm bath would be followed by the hot bath (caldarium) and perhaps a trip to the sweat bath (sudatorium). Finally, the bather cooled down by plunging in the cold bath (frigidarium). A rotunda more than twenty-four meters in diameter anchored the main east-west axis of the bathhouse and is visible on a fragment of the Severan Marble Plan.137 The large circular hall likely functioned as a central circulation space for visitors to greet friends and with its six exits provided a means to communicate to the various appended rooms. It possibly served also as the location of the frigidarium.138 The ruins of this once-grand hall as envisioned by the artist Piranesi in 1762 capture the essence of what remains visible today (Figure 32).139

32. G. B. Piranesi, detail of the Baths of Agrippa from The Campus Martius of Ancient Rome (1762). (Private collection)

Bathhouses were raucous places, not locations for quiet contemplation. Seneca compared the unpredictability of life to the atmosphere of a bathhouse: “Sometimes things will be thrown at you, and sometimes they will strike you by accident.”140 Living near a bathhouse, Seneca complained of the noise emanating from within, providing an extraordinary picture of the bathing experience in Rome:

So picture to yourself the assortment of sounds, which are strong enough to make me hate my very powers of hearing! When your strenuous gentleman, for example, is exercising himself by flourishing leaden weights; when he is working hard, or else pretends to be working hard, I can hear him grunt; and whenever he releases his imprisoned breath, I can hear him panting in wheezy and high-pitched tones. Or perhaps I notice some lazy fellow, content with a cheap rubdown, and hear the crack of the pummeling hand on his shoulder, varying in sound according as the hand is laid on flat or hollow. Then, perhaps, a professional comes along, shouting out the score: that is the finishing touch. Add to this the arresting of an occasional roysterer or pickpocket, the racket of the man who always likes to hear his own voice in the bathroom, or the enthusiast who plunges into the swimming-tank with unconscionable noise and splashing. Besides all those whose voices, if nothing else, are good, imagine the hair-plucker with his penetrating, shrill voice, – for purposes of advertisement, – continually giving it vent and never holding his tongue except when he is plucking the armpits and making his victim yell instead. Then the cakeseller with his varied cries, the sausageman, the confectioner, and all the vendors of food hawking their wares, each with his own distinctive intonation.141

Crowded with patrons seeking an afternoon of relaxation, socializing, and exercise, Agrippa's baths provided a source of employment for many. As Seneca notes, sellers of food and drink would have strolled the halls, and bathers could buy oils and other bathing necessities, rent towels, and hire services such as massages.142 Shops provided additional goods for bathhouse guests. The baths themselves needed a large work force, both freedmen and slaves, to supply and store wood for the furnaces, maintain the machinery and fistulae, launder hundreds if not thousands of towels each day, clean the rooms, and generally maintain the structure.143 Workers would have arrived early and stayed late seven days a week, keeping the central Campus Martius a constant center of bustling activity. Agrippa's bathhouse would have also attracted prostitutes, who often plied their trade in and near the baths.144 As noted in Chapter 4, the third-century C.E. emperor Elagabalus was purported to have rounded up prostitutes from the bathhouses as well as other public places.145 Describing a floating orgy on the Stagnum near the Agrippan baths during Nero's reign, the writer Tacitus noted that “on the quays of the lake stood brothels, filled with women of high rank; and, opposite, naked harlots met theview.”146

While Agrippa's baths were clearly successful, Romans continued to use the smaller, privately run bathing establishments such as the Balneum Claudii Etrusci supplied by the Aqua Virgo and known for the richness of its marbles.147 Notwithstanding the popularity of the Thermae Agrippae and the presence of many smaller bathing facilities, the emperor Nero built Rome's second major bathhouse in the Campus Martius about 400 meters northwest of Agrippa's baths. Why Nero selected a site so close to the Agrippan complex on which to establish his own thermae is unknown, although three factors could have played a role. At the time, this area of the Campus Martius remained mostly open and undeveloped, the baths were near a ready supply of water from the Aqua Virgo, and they opened north on a road that ran west from the Via Flaminia in the direction of the Tiber, possibly connecting to the bridge known later as the Pons Neronianus.148 Whereas the Baths of Agrippa had small areas for exercise within thethermae walls, Nero's had a large Greek-style gymnasium integrated with the bathhouse.149 Later, Domitian would build a facility just next door for viewing Greek-style games, the Stadium of Domitian. The configuration of Nero's structure is uncertain and may have comprised an “irregular grouping of buildings” that took advantage of Agrippa's gardens and the Stagnum in much the same way as did Agrippa's baths.150

The opening of the baths by Emperor Nero was a grand affair, underscoring the significance of these new imperial bathhouses in Rome's social life. To celebrate its completion, the emperor staged games called the Neronia with three contests: gymnastics, horse racing, and music. The gymnastic contest was held not in the bathhouse itself but in the Saepta Julia, as discussed in Chapter 4.151 As part of the celebration, Nero awarded all members of the Senate and equestrian class with bath oils.152 Not all Romans appreciated Nero's generosity, however. A philosopher named Demetrius entered the bath's gymnasium on opening day and commenced a tirade “against people who bathed, declaring that they enfeebled and polluted themselves; and he showed that such institutions were a useless expense.”153 Luckily for Demetrius, the emperor was singing in a tavern next door to the bathhouse and did not hear the outburst, or Demetrius's death would have been immediate. The story did, however, make its way to Nero's friend Tigellinus, now head of the imperial guard, who had Demetrius banished, claiming he “had ruined and overthrown the bath by the words he used.”154 Others who were not fans of Nero nevertheless enjoyed his baths. Remarking on the contrast between Nero and his eponymous thermae, Martial wrote: “What was worse than Nero? What is better than Nero's warm baths?”155

After the construction of Nero's complex, no other major bathhouse was built in the Campus Martius for more than a century and a half. Emperors Titus, Trajan, and Caracalla sited their imperial baths elsewhere in the city. Additionally, private bathhouses continued to play a significant role in the Roman bathing experience. The fourth-century C.E. regionary catalogs note that the number of balneae had grown almost sixfold from the time of Agrippa, with sixty-three scattered throughout the Campus Martius alone. Part of that growth may have come from the emperor Alexander Severus, who made sure in the early third century C.E. that every Roman neighborhood had at least one private bathhouse.156 In 227 C.E., however, Alexander Severus decided to make use of Nero's 163-year-old structure to impress his own major mark in the Field of Mars: he renovated and renamed the baths after himself and created a parklike nemus or garden in the vicinity, an action that may have been inspired by the similar projects of Agrippa in that sector of the plain. Although the Aqua Virgo likely fed the earlier bathhouse, its water resources must have been inadequate by the third century C.E. to meet the demands of an expanded structure, because we are told in the Historia Augusta that Alexander Severus built a new aqueduct to supply it – the Aqua Alexandrina.157 The aqueduct brought the water from a source almost 18 kilometers east of the city to the vicinity of the eastern gate later known as the Porta Maggiore and then another 3.2 kilometers through the city to the baths.158 Whereas Nero likely built his original facility in empty fields, Alexander had to purchase and raze surrounding buildings in order to add a park to the baths. The once-open Field of Mars now required reclamation to create green space. Whereas Agrippa had given his baths to the public for free use, Alexander Severus imposed taxes to maintain his. He did, however, illuminate his baths so that bathers could enjoy the facilities at night, helping to ensure that the Campus Martius was an area not only for nocturnal work but also for evening entertainment.159

When the expansion and renovation was completed, the baths of Alexander Severus covered more than 22,000 square meters, almost three times the size of Agrippa's baths.160 To ensure enough wood was readily available to heat the enlarged facility, the emperor designated entire forests solely for its use.161 On the basis of plans of extant ruins drawn by the eighteenth-century architect Palladio, it is thought that the patrons entered from the north into a courtyard with a large swimming pool. Colonnaded courtyards for exercise flanked the pool. The building was symmetrical with the east-west axis anchored by the frigidarium and the tepidarium. The caldarium may have protruded from the center axis on the south side.162

The Campus Martius's two major bathhouses continued to serve Rome's public bathing needs for centuries. Agrippa's baths were repaired after suffering damage in the fire of 80 C.E. and restored again as late as 345 C.E. After Alexander Severus expanded Nero's bathhouse, those baths likely continued in operation until the sixth century C.E., when invading Goths cut the water supply and the Roman general Belisarius blocked with masonry the aqueducts, including the Aqua Virgo, to prevent their use as a means by which to enter the city.163 With aqueducts destroyed or blocked, baths were forced to close. Drinking water was obtained by digging wells.164 The aqueducts were functioning again within about sixty years, but it is unclear whether they then supplied the former imperial bathhouses.165 Only the Virgo's connection to Rome has continued into the modern era, supplying fresh water daily to the beautiful Trevi Fountain just to the east of the ancient eastern boundary of the Campus Martius. Agrippa's baths later became a center for lime burning, with marble from surrounding ruins thrown in the ovens and cooked down to a chalky powder that was then remixed for later construction.166 Much of the ruins of the Neronian/Severan baths were incorporated into other structures, in particular the fifteenth-century Palazzo Madama, now the location of the Italian Senate. Substantial remains of the structure were visible in the seventeenth century, and a few glimpses of its outer walls remain, as well as large columns discovered below street level (Figure 33).167

33. Columns from the Neronian/Severan baths (Via di Sant’Eustachio, Rome). (Photo: Paul Jacobs)

By the third century C.E., the Campus Martius was drained of its low marshes and filled with structures, and stagnant pools were replaced with the Aqua Virgo's cold, fresh water. These alterations to the environment did not end the risk of malaria, however. Ironically, this is possibly due to the fact that Anopheles mosquitoes that carry human malaria prefer clear, well-oxygenated water.168 That keen observer of nature, Pliny the Elder, noticed that “culices,” a term that can mean mosquitoes, liked to buzz around irrigated gardens, a problem that would have applied to the Campus Martius's parks and quadriporticoes with their well-watered trees and exotic plants.169 The large Stagnum as well as the slow flowing Euripus Virginus also must have attracted mosquitoes.170Even workers in an area such as the Roman Forum, despite it being well drained and built up by the late first century B.C.E., were at risk of fever, according to the Roman writer Horace.171 Whether the mosquito problem impacted traffic to the Campus Martius in the later summer when the risk of malarial infection peaked is unknown, but it is doubtful that any one, low area of the city was worse than another. Wealthy nobles owning extramural country estates could flee the hot and mosquito-infested city altogether, but such an option did not exist for most inhabitants of the capital. Later visitors to Rome warned of the risk of mosquito bites in the warm weather months. The English writer Horace Walpole noted in 1740, “There is a horrid thing called the malaria, that comes to Rome every summer, and kills one, and I did not care for being killed so far from Christian burial.”172

Water from Afar

Water had not only a significant physical presence in the Campus Martius but a metaphorical one as well. The war god's field was filled with reminders of military success on the waters of the Mediterranean basin. The most obvious, perhaps, was the presence of warships and their berths. Along the Tiber's edge in the western Campus Martius stood the military ship sheds or navalia. First mentioned in 179 B.C.E., they were expanded over the years and were significant structures with peaked roofs sheltering each ship.173Romans would line the riverbank to watch Roman war vessels make their way to the offloading ramps carrying extraordinary booty from foreign lands. Enemy vessels captured at sea and brought to the city for display afforded another spectacle for Rome's inhabitants.174

Numerous temples in the Campus Martius, vowed to the gods during skirmishes on the seas, memorialized past naval triumphs. Some of the honored gods had mythological connections to water or war. Following the defeat of the Carthaginian fleet off of Sicily in 260 B.C.E., the Temple of Janus was dedicated in the Forum Holitorium at the southern end of the Field of Mars near the Pons Fabricius, the bridge crossing to the Tiber Island.175 At the time the temple was built, Rome did not have a “sea” god, and Janus's association with water crossings and bridges could have suggested to a victor in naval warfare that he was an appropriate deity to honor with a shrine.176

As discussed in Chapter 3, a temple of the nymph Juturna was vowed in 242 B.C.E. in connection with the defeat of the Carthaginian navy in a battle that ended the First Punic War. The temple was located in the central Campus Martius as was another, the Temple of Vulcan, which commemorated the Roman fleet's landing and taking of the Aeolian island of Lipari.177 A vow made in the successful naval battle against Antiochus the Great resulted in the construction of the temple of the “Lares of the Sea” with its lengthy inscription describing the enemy's defeat, including the capture of forty-two ships and all of their crew.178 A temple of Neptune, a protector of waters, may have stood along the edge of the Circus Flaminius.179

Not surprisingly, nautical motifs were visible throughout the Campus Martius. At the field's southern end, the Tiber Island was surmounted by a wall fashioned to look like a ship's stern.180 The Temple of Neptune was decorated, according to Pliny the Elder, with Nereids riding the backs of dolphins, Tritons, and numerous sea creatures.181 A frieze from a large base or altar thought to have been in the vicinity of the temple in the Circus Flaminius displayed a marine thiasos (celebratory procession) and, possibly, featured Amphitrite and Neptune (Figure 34).182 Wedged between the Pantheon and the Baths of Agrippa, a large rectangular building, known as the Basilica of Neptune and the Stoa of Poseidon, was decorated with sea creatures and dolphins (Figure 35).183 The basilica possibly had an entrance on the east side, opening onto another structure with symbolic connections to the sea. Decorated with paintings relating the adventures of Jason and the Argonauts, the Porticus Argonautarum offered visitors to the marble space a mythological history of the sea routes now traveled by Roman cargo ships.184

34. Detail of the decorative frieze of marine thiasos from the Paris/Munich reliefs (formerly known as the Altar of Ahenobarbus) (first century B.C.E.), Glyptothek, Staatlich Antikensammlung, Munich, Germany. (Photo: Foto Marburg / Art Resource, New York)

35. Detail of the decorative frieze from the Basilica of Neptune, Via della Palombella, Rome. (Photo: Paul Jacobs)

To the east of the Saepta Julia were the temples of the Egyptian gods Isis and Serapis. Here the waters of the Nile, transported from Egypt in jars, were used in cultic practices.185 In close vicinity to the temples stood statues of the water gods, Nile and Tiberis (Figures 36 and 37). Later perhaps, three others, including the god Oceanus, were added.186 Interpreted as the personification of these rivers in full flood, the statues of the Tiber and the Nile possibly date to the early second century C.E. and display well-understood attributes of the two rivers.187 The Nile god reclines with a sphinx and a cornucopia at its elbow and crocodiles under its legs. Sixteen children, perhaps representations of Roman provinces or conquered nations, climb about his trunk and limbs.188Pygmies and wildlife are carved in the sides and back of the base. Like Nile, Tiber rests by a horn of plenty. Here, however, the sphinx is appropriately replaced by the she-wolf nursing Romulus and Remus. A base relief possibly displays Aeneas as part of the foundation legend of Rome as well as workers unloading cargo from riverboats.189 As Swetnam-Burland has noted, each of these statues viewed by both perambulators in the park and participants in the Egyptian cults “blend[ed] complementary threads of visual, historical, and mythic traditions into a single artwork that embodies positive associations between the river and those who depend on it for life and livelihood.”190 Their placement in the Campus Martius where river floods were more than a theoretical issue would not have been lost on the imperial viewer.

36. Nile River (early second century C.E.?). Braccio Nuovo, Museo Chiaramonti, Vatican Museums, Vatican State. (Photo: Album / Art Resource, New York)

37. Tiber River (early second century C.E.?). Louvre, Paris. (Photo: RMN-Grand Palais / Art Resource, New York)

As the marble cornucopia at the Nile god's elbow represented the foreign bounty now flowing to Rome, so, too, the daily commercial traffic floating along the Campus Martius's meandering western border provided a constant reminder of Rome's supremacy over the Mediterranean and the riches under its control. It also placed the Field of Mars literally within the stream of commerce. The legendary grain of Tarquinius Superbus that washed downstream from the Campus Martius to form the Tiber Island wassubstantially multiplied centuries later: more than one-half million tons of grain was brought up the Tiber to Rome annually from farmlands throughout the empire.191 Although, as Pliny noted, the Tiber was “accessible to ships of the largest size from the Italian sea,” goods would be off-loaded at the port of Ostia and then barged upriver to Rome on smaller vessels.192 Stored in warehouses, or horrea, on the edge of the Campus Martius by the Forum Holitorium, the grain was carried to the Transtiberim to be fed into the mills that used the Tiber's flow to operate the millstones that ground the wheat. The flour was then taken across the river and moved along the roads of the Campus Martius to be distributed to Romans from the Porticus Minucia Frumentaria.193 Over eighty thousand cubic meters of wine entered the city annually, much of which was transferred to the docks along the Campus Martius, and beginning with the reign of Aurelian (r. 270–5 C.E.), was transported across the Field of Mars and up the Quirinal Hill for distribution from the portico that ran along the Temple of Sol.194 Tons of foreign marble were barged to the area around the Pons Aelius to be cut and moved to construction sites within the city.195 Wine from Greece, exotic marbles from Anatolia, granite from Egypt, and even wild animals from Africa removed from the holds of river vessels docking at the Tiber's banks along the Field of Mars served to emphasize that the Mediterranean was just one more road that led to Rome and that the Campus Martius was an important way station for the empire's riches.


No other area of Rome faced greater risks from the impact of water nor offered greater opportunity to employ it for the benefit of its citizens than the Campus Martius. The low, marshy, and open plain that lay prone to the Tiber's floodwaters was at first defenseless to the seasonal inundations, but it made little difference when the Field of Mars served primarily as a seasonal mustering ground and voting precinct. Winter floods and summer mosquitoes could be avoided. As the Romans sought to make greater use of the space, however, they had to shape the landscape in an attempt to mitigate damages and dangers. Drainage channels, buildings of brick and concrete, and use of fill dirt were deployed to resist the Tiber, albeit with modest success. Despite such efforts, the Campus Martius continued to flood and yet the Romans continued to build; the space was simply too important to leave undeveloped. Even the threat posed by malaria-bearing mosquitoes in late summer did not dissuade the Romans from turning the space into a year-round venue for entertainment and commerce. Grain, marble, and wine moved down the gangplanks on the Tiber's edge and trundled in carts through the streets of the Campus Martius. Much of the marble moved only a few hundred meters to be used to construct temples, porticoes, and theaters whose erection in the Field of Mars continued, unrelenting.

If the first grandiose bathhouse was to be built anywhere in Rome during the Augustan Era, it made sense to locate it where the other Agrippan projects were underway, on land controlled by Augustus's admiral. Yet this meant creating an enormous and costly infrastructure to bring in a secure source of fresh water and then devising a system to channel it to the Tiber. In fact, using those channels to meet the water needs of development across the Tiber made the whole scheme practical. These goals were accomplished with the completion of the Aqua Virgo in 19 B.C.E. and the construction of the Stagnum, the Euripus Virginis, the Euripus Thermarum Agrippae, and other conduits. Agrippa's dedication to engineering improvements made the Virgo's water available for bathing, aquatic displays, swimming, and other water-related activities in the Field of Mars and beyond. Fed by the Virgo, Rome's first imperial baths, followed by a second bath complex and another aqueduct, helped ensure that the Campus Martius, once an occasional venue for public gatherings, was a daily destination for work, residency, and relaxation. Where stagnant water once saturated marshy soil, by the imperial era fresh spring water filled bathing pools and coursed through channels of concrete carved into manicured parks, wending around columned temples and theaters.

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