Engineering Rome

Acqua Paolo and Il Fontanone

Acqua Paolo and Il FontanoneRome’s Forgetten Aqueduct

tprusa20 tprusa20 Sep 29, 2017

1. Introduction

Water: the source of life. The Roman Empire: arguably the greatest civilization the world has ever seen. In the modern era, the two are intertwined. It is impossible to mention the Roman Empire, and in particular Rome, its historic capital, without mentioning water, and with water, aqueducts.

As one of the first, large-scale water distribution technologies, aqueducts were a major source of economic and social prosperity for the Empire from their construction beginning in the Republican Era (509 B.C.-27 B.C.), through the Imperial Era (27 B.C.-530 A.D.), with restorations in the Middles Ages and the Renaissance (through the early 1600s). Some, such as the Aqua Virgo in Rome, continue to function to present day. While at times neglected, the aqueducts of the Roman Empire dot the landscapes of dozens of countries and hundreds of communities in the Mediterranean (see Figure 1). Most importantly, aqueducts provide a proof of concept of large-scale water distribution that enabled the further development of technologies that continue to shape the water resources of the world today.

Figure 1: Map of all known Roman aqueducts (Romaq)

This paper focuses not on the grand scale of aqueducts as a technology or their impact on the Roman Empire, but on a single aqueduct and its often-forgotten story. As a case study of late Roman hydraulic engineering, the aqueduct is an excellent example of iterative design and the reuse of existing infrastructure that continues in the city today. To begin, we need to focus on the capital of the Empire, Rome itself.

2. Background

Within the city of Rome, 11 historic aqueducts supplied the city with water. Of those 11 aqueducts, nine originate from the areas east and north of the city, bringing water most directly into the eastern half of a city split down the middle by the Tiber River. Despite traveling longer distances from the Apennine Mountains, water sources were large, more plentiful, and easier to control with the grade of the aqueducts bringing water down into the city. Figure 2 shows a map of the historic aqueduct routes and Figure 3 shows a topographical map of Rome and the surrounding region.

Figure 2: Routes of the 11 historic aqueducts of Rome (Aicher, 1995)

Figure 3: Topographical map of Rome. Click to interact (

While it may sometimes seem trivial today, water use in ancient Rome is similar to that of present-day Rome. Exact consumption is tough to compare because ancient Romans used the Roman quinaria, a non-standardized flow measurement. As aqueducts allowed for a municipal water system, Romans used water for domestic purposes, agriculture, and industry. Although Roman homes with individual connections were an anomaly, water-intensive industries such as mechanized mining and power generation didn’t exist, and agricultural irrigation has advanced considerably, per capita water usage was likely similar to today (Kosonen, 2017).

Sadly, most of the research on water usage in the Roman Empire has focused on uncertainties surrounding the quinaria, rather than exploring gross usage data in more depth. One study that attempts to compare ancient municipal with present day use takes empirical flow measurements from aqueducts that were still running, calibrates a quinaria in modern units, and then uses numbers from Roman engineer Frontinus’ //De aqueductu// to compare municipal data in England and the eastern United States; Table 1 summarizes this anaylsis (Morgan, 1902). While Morgan, the study author, worked over 100 years ago and classifies his ultimate estimates as rough at best, he conducted one of the only studies to date attempting gross water usage comparisons. Morgan’s study also places Rome’s per capita usage in 94 A.D. at the low end, but within reason, of per capita usage at the turn of the 20th century.

Beyond the quinaria and the precision with which we know historic population data, Morgan’s largest doubts come from the lack of expansion in Rome’s water supply as its population peaked around 100 A.D. Part of this skepticism comes from Morgan and other scholars’ incomplete understanding of the total number of historic aqueducts serving the city. While relying on Frontius, Morgan and his contemporaries missed the construction of two poorly documented aqueducts completed after Frontius compiled his Da Aqueductu that continued to expand the city’s water supply into the third century A.D. One of these “forgotten” aqueducts from after Frontius’ writing was the Aqua Traiana, later known as the Acqua Paolo, that serves as the focus of this article.

Table 1: Municipal level average daily consumption in 1901 (Morgan, 1992)

City. Average daily consumption in gallons. Per capita consumption in gallons.
Cambridge 7,520,976 80.7
Borough of Brooklyn, N.Y. 97,000,000 83
Baltimore 56,000,000 100
Boston 101,492,000 120
Boroughs of Manhattan
and The Bronx, N.Y.
275,000,000 134
Chicago 322,599,630 161
Philadelphia 279,975,453 211.9
Rome (c. 94 A.D.) 84,000,000 84

By the mid-1500s, Rome and its aqueducts had fallen into disrepair. The city only had “two barely functioning aqueducts, two or three public fountains, a handful of dismal public cisterns and wells, and a murky turgid river flowing through the center of town” (Rinne, 2010). Once a city of over 1,000,000 people, Rome’s population fell below 50,000, and Rome needed new sources of water to bring agriculture, industry, and above all people back to the city (Hodge, 2002). Once begun, the impacts of both public and private water in the city were immediate, immense, and integral to the redevelopment of Rome.

Aside from allowing increased domestic use, repairing historic aqueducts allowed for increased water security for the city and the development of water-related public works. Heavily tied to domestic use due to public distribution through fountains, public works allowed water distribution to become a symbol of prestige, wealth, and power and motivated the renovation and extension of old aqueducts in the Middle Ages and Renaissance (Rinne, 2010). What may have began as the resurgent Catholic Church’s desire to leave a mark on the city landscape resulted in an abundant, revitalized city water supply in the early 1600s that sets the stage for our lost aqueduct of Rome.

3. Acqua Paolo

It should be noted much of the research regarding Aqua Paolo and it’s construction comes from Katherine Rhinne’s exhaustive “Waters of Rome” project that she has turned into both a book, “The Waters of Rome: Aqueducts, Fountains, and the birth of the Baroque City”, and an interactive site where she has compiled numerous invaluable sources for this paper. The following section would have been impossible to compile without her research. The historical narrative of Acqua Paolo comes from Rhinne’s work unless otherwise noted.

Acqua Paolo was the last of three major aqueduct renovations carried out by the Catholic church during the late 16th and early 17th centuries in Rome. After the return of the papacy to Rome from Avignon in 1376, the Catholic church returned to a broken city. Along with revitalizing the spiritual church, major infrastructure upgrades were needed to make the city habitable again.

Pope Paul V, of Acqua Paolo (literally, “Paul’s waters”), was not the first or the last Pope to undertake major water infrastructure work. He began his papacy in 1605 by following in the footsteps of Popes Sixtus V and Clement VIII by restoring and extending the distribution of Acqua Felice throughout the city. Best known for his debates with Galileo Galilei, Pope Paul V was prolific in extending the water system of Renaissance Rome. His first extensions of the Acqua Felice system were primarily in the Caelian and Quirinal Hills with both new lines and fountains in church squares (see Figure 4).

Figure 4: Expansions of Acqua Felice (Rinne, 2010)

After extensions of the Acqua Felice, Pope Paul V looked to build what at that time would be a third aqueduct for the city to supply the Vatican, Borgo, and Trastevere with water (see Figure 5). While primarily motived by the desire to once again have fountains on St. Peter’s Square, Pope Paul V was also concerned with supplying major Cardinals beneath him, including his nephew Cardinal Scipione Borghese, with water in their palaces in the Borgo region just east of the Vatican.

Figure 5: Initial Acqua Paolo Distribution System (Rinne, 2010)

Existing water supplies and the overall condition of Trastevere, Borgo and the Vatican, and Janiculum Hill could not have been more different at the turn of the 17th century when Pope Paul V was elected and began looking to bring water to the area. Figure 6 shows a snapshot of the hydraulic infrastructure of the west half of the city in 1600. Trastevere (literally, “other side of the Tiber”) was a densely-crowded, middle-class neighborhood. In a perennial flood plain, it was flat enough to have water distributed to it from Acqua Felice across the Tiber at different periods in Rome’s history. The extension of Acqua Felice by Clement VIII shown in Figure 4 was one of many aqueduct river crossings that existed prior to the construction of Acqua Paolo. The exact course varied as bridges carrying aqueduct water were destroyed by the Tiber over time. Pottery mills, grain production, and the river port of Rome were the major industries of the neighborhood. At the start of the papacy of Pope Paul V, the area relied on the Tiber River for all of its water supplies.

Figure 6: Roman Water Infrastructure in 1600. Click to interact (Aquae Urbis Romae)

The Vatican, and neighboring Borgo to the east, were better served and had small sources of spring water. The Vatican drew from a spring at the Belvedere Cortile and had enough water to supply small fountains in St. Peter’s Square, but Pope Paul V wanted a steady source of water for more lavish papal fountains. The Borgo drew from a small spring at the Porta Cavallegari that fed a public drinking fountain, but also relied on water from the Tiber.

Lastly, Janiculum Hill was a relatively remote, sparsely populated hill with city officials and church elite that lived beyond the Borgo. Across the river and outside of the seven historic hills of Rome, it remained important because of it’s proximity to the Vatican. Most inhabitants, largely cardinals and monks, resided in a handful of palaces, monasteries, and vineyards. Most residents relied on private wells or, for those wealthy enough, water manually carried up the hill.

By supporting the development of water infrastructure in the city of Rome, Pope Paul V not only cemented his legacy as a builder, but contribued to the physical form of the city. In particular, his “new” water sources revived the Travestere neighborhood by supporting the port, Ripa Grande, and grain mills on Janiculum Hill (Aicher, 1995). In addition to a major fountain in Il Fontanone, Pope Paul V also planned a straight, central street running from Il Fontanone to Ponte Sisto at the Tiber (Heilmann, 1970). While the technical difficulties of managing Il Fontanone alone ensured the road from Ponte Sisto never became reality, the Acqua Paolo distribution lines influenced the development of Travestere industries well into the next century. At first by powering grain mills on the slopes of the Janiculum and later moving the Port of Ripa to Travestere, Acqua Paolo water determined where and how industries, fountains, and the neighborhood itself could be built (Heilmann, 1970).

3.1 Construction

Initial scouting for suitable sources for Acqua Paolo began in 1605 at the start of Pope Paul V’s papacy. While there is some debate over when he began looking to build a then third aqueduct for the city, the lengthy timeline required for such a project, as well as the pressing water situation at the Borgo, suggests preliminary work for the aqueduct began when he took office (Freiburg, 1991). Some scholars claim surveying and scouting only began after the more shovel-ready work of extending the Acqua Felice was completed in 1608.

Pope Paul V began by sending a Cardinal and a representative from the Vatican Bank to search for springs north of Lake Bracciano that were rumored to have supplied Aqua Alesietina. As mentioned previously, Pope Paul V and his construction team likely relied solely on the writings of Frontius and would have known Aqua Alesietina as the only previous aqueduct feeding the west side of the Tiber. He hired on Flemish engineer Pompeo Targone as a supervisory engineer and began by paying him to research and visit ongoing and recently completed water projects across southern Italy. As the first example of a Roman water infrastructure project conducting contemporary research, Rinne suspects Pope Paul V intended at the outset to outdo the scale of the Acqua Vergine and Acqua Felice with the Acqua Paolo. In the end, it was largely his good fortune at finding the remains of the Aqua Traiana that made the new line possible.

3.2 Construction Engineering

From a construction engineering point-of-view. The Acqua Paolo was an immensely interesting project. At the outset of the project, Pope Paul V had his work cut out for him. Looking for the remains of a mythical aqueduct, with no money, and only a few skilled aqueduct craftsman remaining from the repair of the Acqua Felice, he went to the Roman Council to pitch his project.

The initial financing structure Pope Paul V gave to the Roman Council most closely resembled an Agency Construction Management style contract we would be familiar with today. This, or any modern project delivery method, is muddied by less distinct roles any one entity played in the project. To begin, Pope Paul V most directly filled the role of owner in the project. As he drove the initial project schedule and hired the presumed construction manager (Pompeo Targone), in today’s world he would be the owner. Targone, as the “supervising engineer” would serve as both a construction manager and design engineer. He would work with a team of architects in design, but would head construction and hydraulics work.

Our model breaks down when we start considering the role of the Roman Council (who had the authority to raise taxes) in financing the project. As a public works project benefiting the city at large, Pope Paul V initially asked the council to cover half of the construction costs and to acquire the springs and land (identified by Targone) for the project. The Council would also be in charge of construction cost overruns. So while Pope Paul V would get water to the Vatican and his name on the aqueduct, the Roman Council carried a lot of risk. See figure 7 for a diagram of the initial project delivery method.

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Figure 7: Diagram of initial project delivery method proposed by Pope Paul V (author figure)

As history thankfully shows, the relationship between the Pope and the Roman Council was more of a two-way street than it looked from the outside. Pope Paul V initially proposed the project at about a third of the expected cost and the Council balked. In charge of financing cost overruns, the Council reportedly went as far as having a secret meeting to come up with a suitable response to the Pope. Pope Paul V, possibly anticipating the Council’s response, came back to them with a different proposal the next time they met.

Pope Paul V’s revised project delivery method resembled a Design-Build-Finance-Operate style contract. Under his new plan, the Roman Council was in charge of the entire construction and operation costs, but would also have the authority to sell, at a fixed price, any remaining water after the Vatican and public fountains were supplied. After the Roman Council accepted, Pope Paul V appointed Giovanni Fontana, a construction supervisor from the earlier Acqua Felice, to work alongside the architectural team. Paul Targone continued to work on the project, but was no longer involved in construction. Pope Paul V also created a committee to oversee Operations and Maintenance divided along the three topographical distribution areas of the aqueduct. See figure 8 for a diagram of the final project delivery method.

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Figure 8: Diagram of final project delivery method proposed by Pope Paul V (author figure)

4. Il Fontanone
Il Fontanone, literally “the big fountain,” was constructed at the final connection of Acqua Paolo to Janiculum Hill in 1614. A massive marble structure once visible from the Tiber, it stood as a grandiose testament to Pope Paul V and the revival of Rome until the completion of the Trevi Fountain in 1762 (see figures 9-12). While the open basin design of Il Fontanone is not original, many sources point to Il Fontanone (and the Moses Fountain of the Aqua Virgo) as influencing the later design of the Trevi Fountain. While eventually outshining Il Fonantone — which deserves the praise it receives in its own right — the art, architecture, and history of the Trevi Fountain are sadly outside the scope of this paper.

Figure 9: Il Fontanone on Janiculum Hill (author photo)

Figure 10: Facade of Il Fontanone (author photo)
Figure 11: Inscription of Il Fontanone (author photo)
Figure 12: Spolia of Il Fontanone (author photo)

Of the fountains installed in Rome, there were three major types: civic, semi-public, and belvatore. Each served a different purpose in the history of Roman water supply and are again deserving of their own unique analysis. Of these, Il Fontanone of Acqua Paolo was a civic fountain that served the practical purpose of ending the Acqua Paolo when it entered Rome. As such, it is also known as a mostra, or terminal, fountain. Located well away from the city center, the fountain was available to the public into the 1700s. Eventually, ordinances were passed against bathing in the basin and the structure was ringed with marble columns to prevent horses from walking up to it (Aicher, 1995).

Placing a fountain at the end of an aqueduct served a number of purposes. First, with the maximum available head, aesthetic displays of arcing water were easiest to pull off. Even with an incomplete knowledge of hydraulics, Roman architects and engineers knew how to maximize open channel flow at the end of an aqueduct before it entered the city and was distributed throughout the system in smaller quantities. Secondly, as a major infrastructure project, benefactors, such as popes and emperors, wanted acknowledgment of their accomplishments and contributions to society. The larger and more ornate the display, the more memorable it would be. Lastly, fountains often dovetailed into castellums, or distribution tanks, for the beginning of municipal water distribution within the city. See figures 13-14 for the location of the Il Fontanone castellum access point. While flows varied seasonally and fluctuated due to maintenance on systems tens of kilometers long, fountains had to be designed to cascade with minimal seasonal flows.

Figure 13: Il Fontanone castellum (author photo)
Figure 14: Behind Il Fontanone. Left is the superstructure of the fountain and another gate to the castellum. Right is the entrance to a private residence (author photo)

4.1 Engineering Challenges

When Il Fontanone was first tested at full pressure during construction, the initial hydrostatic pressure destroyed one of the five marble fountain basins and ran down Janiculum Hill. It took five days to divert the flow to an area by the Vatican and seven months before repairs were finally made to bring the water into the fountain at a safer, more consistent velocity. Before the leaking water could be redirected, the fountain flooded the San Cosimato area of Trastevere and resulted in the failure of retaining walls at the base of Janiculum Hill. Problems with maintaining Il Fontanone continued into the early 1700s with documented flooding at San Pietro church in Montorio in 1690 and 1731 (Rhinne, 2010). While iterative, ultimately the most sustainable solution to the high incoming pressures of Acqua Paolo was to install additional break pressure tanks as water descended the Janiculum (Aicher, 1993). In the late 1670s, water-powered grain mills were eventually installed along the base of Janiculum Hill before flowing out to Trastevere and across the Tiber (Aicher, 1993). See figure 14 for an example of a current retaining wall beneath Il Fontanone.

Figure 15: Retaining wall located on the slopes of Janiculum Hill today (author photo)

4.2 Cultural References

Despite being far from the tourist center of the city, Il Fontanone has not been forgotten in Roman history. The fountain has made an appearance in numerous poems, music, and movies, including as recently as 2015’s Spectre.

The most famous musical piece about Il Fontanone is titled “The Fountains of Acqua Paolo” and was composed by American Charles Griffes in 1915. Click on the video below to listen to the song.