From the moment a person wakes up in the morning until they get ready to go to sleep, the average person interacts with water infrastructure countless times. Whether this is to take a shower, wash dishes, or hydrate, fresh, drinkable water is something the developed world can take for granted. A whopping 214 liters per day are supplied per person in present-day Italy for its citizens(ISTAT 2024).

Ancient Romans also found their solution to their water needs thousands of years ago in the form of aqueducts as seen in Figure 1. These aqueducts delivered up to a million cubic meters per day (Aldrete 2004) per day. This water was used for public baths, fountains, or private residences. However, this large availability of water depends on an equally large system for disposing of used water. This is where the ancient Romans found another solution to their water needs: the Cloaca* Maxima*, ancient Rome’s oldest and biggest sewer.

This article will aim to explore the history and significance of the Cloaca Maxima as it evolved with the city of Rome and its needs until the fall of the Roman empire as well as an estimate for the cost of building the Cloaca Maxima.

## Construction and early use of Cloaca Maxima

When walking through the eternal city of Rome, one can readily see that the city is constantly building upon itself or repurposing buildings rather than removing a building and making a new one. The sewers of ancient Rome were no different. The Cloaca Maxima was not initially built with the express purpose of carrying contaminated water outside of the city but rather served as an open-air canal that brought water into the Roman Forum from the Tiber River for easy transportation. In this initial iteration of the Claoca, the focus was not to provide anything specific to the canal other than a consistent waterbody in an area prone to large changes in water levels due to flooding (Hopkins 2007).

The practical advantage this could have to pre-imperial Rome is having a level waterway that is at a lesser risk of flooding and is less affected by the Tiber River’s natural flooding. Additionally, since it was fresh water, the city had access to a constant stream of usable water. Figures 3 and 4 show the drastic change in the topography that the Roman Forum underwent to construct Cloaca Maxima. Such a drastic change would surely have required extensive amounts of material, labor, and planning. Proved to be an indicator of the future infrastructure developments the Roman Empire was capable of.

Building a large canal required several logistical hurdles to overcome during the construction process. The first of these challenges was leveling out what would become the Roman Forum as seen in Figure 4. Accomplishing this would require labor, materials for infill, and time for transport before any part of the canal was built. Once this was done, the Cloaca was ready to be built.

Tuff was the material chosen to line this new canal with a thickness of 0.3 meters and a height of 1.25 meters. The canal would then have over a meter width between both walls to allow water to flow through into the Tiber (Hopkins 2007). Building with blocks of this magnitude raises a major question: was this the best path forward despite the logistical requirements needed to use stones of this size?

Hopkins argues that the tuff used to build the lining of the canal was due to more than just one reason. While there were varying examples of canals that size existing without any lining, the Romans wanted to prevent any erosion of the surrounding infill. Additionally, Having the canal lined with large, heavy blocks could be seen as a sign of dominance over the natural world. By the 6th century BC, the Cloaca Maxima had finished construction and provided a foundation for Imperial Rome.

Choosing to use tuff was ultimately what led to the longevity of Cloaca Maxima as it is an easily malleable stone with good structural strength. The further down in the ground a structure is, the older it is, and this canal was built along with the terraforming of the land surrounding the Roman Forum. Since the initial scope of Claudia Maxima was to simply be a canal lined with stone, the large blocks provided the perfect base for the additional work to be performed in the future since these stones can withstand large amounts of force as the thick stones are surrounded by land. This is evidenced in Figure 5 taken by Hopkins. We see that the ceilings gave into the weight of the land rather than the bottom lining walls which would have been the original canal.

Changes in the Roman empire would eventually lead to a transformation of the Cloaca Maxima in both its construction and its use into a sewer system that would prove to be as important to Rome as the Aqueducts that provided the city with drinkable water.

## Cloaca Maxima as Rome’s Sewer

By the second century BC, the Cloaca Maxima had gone from an open-air canal to a fully covered waterway (Deming 2020). This transition marked an important transition from a canal that, when combined with surrounding infill, was only meant to control the flow of water into an early example of a working sewer system. Aldrete elegantly describes Cloaca Maxima:

“In their fully developed form, these sewers were impressive engineering achievements made of concrete or even high-quality stone. The capacity of the sewers was also astonishing. Portions of the Cloaca Maxima were more than four meters tall and three meters wide..”

As described by Aldrete, Cloaca Maxima was a project that was constantly growing and changing depending on the needs of Rome since the size described was much larger than that of the original canal at a final length of 1,600 meters. The lack of uniformity in construction materials was due to the constant changes in the sewer. An example of these changes is the various winding paths of the sewer. This is due to the Romans preferring to build new ducts to go around a new building rather than building on top of the sewers due to structural concerns (Hopkins 2007). We can also see these preferences for building new materials used throughout various parts of the sewer with different materials (Hopkins 2007).

Although the use of Cloaca Maxima was a sewer, it was still very similar to the canal it was originally meant to be. Rather than having pipes deliver fresh water to every living space and providing a sewer, Most of Roman society lived in higher-density housing which often did not have any water or sewer access (Deming 2020). If there were to be a sewer underneath homes with no running water, we would see the accumulation of toxic gasses, disease, and unwanted rodents. Bathhouses remained one of the few places with running water and they were open to the public [Aldrete].

During visits to Pompeii and Ostia, there were well-preserved examples of this primitive yet innovative sewer system. In Ostia, there were fully visible latrines, as seen in Figure 7, where people would spend some time going to the bathroom. Additionally, there is plenty of room underneath the latrine for waste to either collect or be pulled with the current of the water in the city. Both cities also show that the Romans had a certain uniformity and best practices for their infrastructure. In all three cities, there were public areas with a system to drain as evidenced by Figures 6-8.

The running water in areas of public use allowed for the full transformation of the Cloaca Maxima from an old canal to that of a sewer. The running water was able to wash away any buildup from these public areas as seen in Figure 8 and carry them to a sewer line. Eventually, these lines would lead to Cloaca Maxima and transport any of the water into the Tiber. While this system is indeed primitive, it did show that Roman leaders deemed cleanliness enough of a priority not only by providing water to wash away public latrines and baths but also by allowing any surplus water to be used for washing the streets. All while making the contaminated water run under the city as pictured in Figure 9.

The fall of the Roman Empire also marked the end of the great water distribution infrastructure. Without Constant maintenance, both the aqueducts and the Claudia Maxima were destined to be forgotten and turn into a part of history.

## The Cost

Cloaca Maxima is truly a feat of early engineering and grew with the Roman empire as its needs developed further. My time in Rome has left me wondering the same question: *How was all of this possible? *While the answer may be easy to answer with religious monuments or the houses of royalty, it becomes something that is not as easily explained with infrastructure. The Baths of Caracalla, the great Roman aqueducts, and Cloaca Maxima all benefitted the public, but the magnitude of these public projects that can only be experienced in person led me to attempt to find an answer to this question for Cloaca Maxima.

### Methodology

Producing an estimate for the Cloaca Maxima comes with challenges. The main one is limited information about the process itself. Due to this, my estimates will start with the original canal as this has clear information about the project’s scope.

For all of the additional work of the project, I will treat the original portion of the Cloaca as a renovation by adding the dome and will assume the remaining length of the Cloaca Maxima was a subterranean project with its ceiling 1 meter underground as Cloaca Maxima is underground during my visit to the Roman Forum.

The works of Janet DeLaine and Seth Bernard will provide my basic values for labor and any context for the building materials involved. DeLaine lists the value of one day’s labor to be 36 denarii as the initial scope of work of the canal cannot be skilled labor. She also lists the density of tuff at 1.7 tonnes/m^3.

“this gives equivalent daily rates for skilled tradesmen and labourers of 61 and 36

denarii. From here we can express all the required rates as multiples of a labourer’s daily pay: a skilled workman earns 1.69 times as much, while the cost of moving one tonne one Roman mile costs 1.44 times as much by ox-cart, 0.26 times as much by river upstream, 0.13 times as much by river downstream, and 0.035 times as much by sea.” – DeLaine

The main assumption for most of this work is that labor is the greatest cost involved since every part of the construction process and the costs to procure were using locally sourced materials. Excavation, transportation, and construction will be calculated with labor and this value will then translate into a cost by using the standard rates for labor. While Bernard does point out the fact that slavery introduces a key confound that cannot be accurately accounted for, assuming that all labor is paid will give a cost to construct that is comparable to modern uses as slavery is not replicable in modern construction.

Bernard used Delaine’s methods and value for the standard pay rate of a laborer. However, Bernard takes this method and modifies it to fit the construction of a wall in the Roman Republic. This era of Rome coincides with the period of major construction and renovation of Cloaca Maxima and will be used for both the canal phase, renovation, and subsequent expansion of the great Roman sewer. (233-38) A quarry shall be assumed to produce 0.75 cubic meters of tufa and a “block of tufa” is defined as 0.12 cubic meters of tufa.

The cost to produce a block of tufa (0.12 m^3) is 0.76 skilled hours and 0.66 unskilled hours including mining and processing. Using DeLaine’s conversion, a block of tufa results in 1.94 unskilled days of labor or 16.17 unskilled labor days per cubic meter of tuff.

### Cloaca Maxima as a Canal

Procuring material for a large-scale construction project has a large influence. Without materials, the job cannot be done, so materials lead time, transportation cost, and workability can all add cost to the final bill. This makes determining the tuff that was used for Cloaca Maxima’s first iteration imperative to the cost to construct since it determines both transportation time and the weight of the material. Seth Bernard points out that *tufo del Palatino *was used into the second century BCE [Bernard]. This specific type of tuff was readily available within 1 km of the Roman capital which makes 1 km a good value for the transportation distance.

Cloaca Maxima as a canal was around 100 meters of canal [Hopkins]. Hopkins also described the original walls as being 1.25 meters tall and 0.3 meters thick. Assuming a consistent thickness on both sides of the canal, the total volume of tuff is 0.75 m^2 times the 100-meter length of the canal for a total of 75 cubic meters of tuff. The density of tuff is 1.8 tonnes/m^3 [Bernard 233-38] for a total of 135 metric tons of tufa. Procuring this much tuff from a local mine before transport takes 16.17 unskilled days per cubic meter. Applying that conversion to our total material cost gives 1,213 unskilled working days.

Transportation can get much more difficult to calculate since this period of construction happens well before the values that are established by DeLaine. Her method of using oxcarts is used because this one is more general for distances, whereas Bernard used a specific project with a transportation route that is different than the canal’s. For this estimate, the values are assumed to be accurate for the labor market at the time. At 1.44 unskilled hours per Roman mile (1.5 km), the cost to transport the material needed to build the canal would be 130 unskilled hours.

Using Bernard’s calculations for the construction of a wall, the cost to build and excavate the 75 cubic meters needed, runs at 0.1814 per block of tufa or 1.51 unskilled hours per cubic meter plus 0.28 *75 in excavation. This brings the cost of construction to 134 unskilled hours.

Adding all costs results in 1,477 unskilled working hours for the completion of the canal.

### Cloaca Maxima as a sewer

Coalca Maxima’s final length stood at 1,600 meters. The largest assumption for this calculation is that all work was done before the imperial era and shortly after the original canal was renovated around 200 BC. Since the canal was built during the Roman Republic, most of the calculations will be done in the same manner as they were done with the canal, albeit with added scopes.

The renovation of the canal would include 100 meters of arches to be built on top of the original. Using Figure # as a reference, we will assume that the arches are built with no additional height. With a radius of 0.5 m and a thickness of 0.3 m the total volume of new arches amounts to 61 cubic meters. Reusing the procurement cost of 16.17 unskilled days, the total cost to procure is 986 unskilled hours. With no excavation needed, the cost of assembling the arch is 92.1 unskilled hours. The total cost of renovating the original canal is 1078 unskilled hours.

For the remaining length of the Coalca Maxima, calculating the volume is a distinct challenge. Due to the growing city, the sewer was not a constant size. We can see this in figure #9 where we see that sizes differed both on the inside and on the outside. To account for variations in size the profile of the sewer will be uniform and be the average of the original canal with an arch and the largest size described by Aldrete as shown in Figure 10. Geometrically, this has an area of 6.3 square meters and has a radius of 1 m and a height of 2 m.

Geometric values for this approximate shape will be the profile area of 6.3 sq.m multiplied by the total remaining length of 1500 m for a total of 9,240 cubic meters of space in the sewer. For excavation, we will add a meter from the top of the sewer for an excavation volume of 12,000 cubic meters, and construction, we will add 0.5 m of thickness to obtain a shell volume of 2,947 cubic meters.

Procuring this much tuff will have similar calculations as the canal with one notable difference. Since the surrounding hills have now been terraformed and the closest mines are used, I am going to use Bernard’s transportation estimates for transportation from a more distant mine. At 16.17 unskilled hours per cubic meter, the cost of materials is 47,653 unskilled hours.

Transportation for a cubic meter from a more distant mine is 2.78 unskilled hours per cubic meter. This makes the total cost for transport 8,193 unskilled hours.

Excavation will be larger than construction since the sewer is now underground with the previously used standard rate, the cost amounts to 3,360 unskilled hours. Construction of the sewers using the established rate of 1.51 per cubic meter totals 4,450 unskilled hours.

The estimated total cost of the expanded portions of Coalca Maxima is 63,656 unskilled hours.

The estimated labor cost for the entirety of Coalca maxima is a total of 65,133 labor hours. At a $20 modern labor rate, the cost is just 1.3 million USD. ISTAT has its current wastewater costs in the magnitude of billions of USD for 2020-23. Even with the much smaller scope of work, the cost to complete Coalca Maxima is a bargain compared to current-day prices.

## Does Spending Pay Off?

What was interesting about this was seeing the effect of building infrastructure around existing systems as opposed to starting in an empty place. My simplified model only assumed that the sewers of Rome were underneath just 1 meter of rock, yet the price of excavation skyrocketed due to the exponential nature of the area. While in Rome, my class toured the new subway line in construction. One of the difficulties that the engineer on site brought up was that the price of navigating around precious ruins and existing infrastructure was the increasing costs of the project.

This brings up a very big question not just for the future of Rome’s infrastructure, but also public works in general: *At what point is the cost too much?* One possible solution is to create and communicate new standards of value engineering with the public so the public can make more informed choices about the benefits of certain infrastructure. However, this can come with its challenges as experts debate what the potential monetary value of a service is. I am personally on the side of maintaining higher standards and building towards compromises, but seeing Rome for the first time has made me wonder if a compromise can start turning into a sacrifice.

While it is rather easy to look at the cost of building both projects and question why certain methods are causing inflated costs, maybe it is better to think of it through a lens of usefulness to its residents. Only time will tell if the current infrastructure projects both in Rome and around the world. Cloaca Maxima was not a good deal for Ancient Rome because of its low cost relative to today’s standards. It was a good deal for Rome because of the way it grew with the empire and kept its residents clean in a way that future cities emulated.

## References

- Aldrete, G. S. (2004).
*Daily life in the roman city : Rome, pompeii, and ostia*. Bloomsbury Publishing USA. Online:https://ebookcentral.proquest.com/lib/washington/detail.action?docID=491587 - Bernard, S. (2018), Building Mid-Republican Rome: Labor, Architecture, and the Urban Economy, Online: https://doi-org.offcampus.lib.washington.edu/10.1093/oso/9780190878788.003.0004
- Delaine, J. (2002). “BRICKS AND MORTAR Exploring the economics of building techniques at Rome and Ostia”,
*Economies Beyond Agriculture in the Classical World*(Vol. 00009). Routledge. Online: https://dx.doi.org/10.4324/9780203204467-15 - Deming, D. (2020). The Aqueducts and Water Supply of Ancient Rome.
*Groundwater*58, no. 1: 152–161. https://doi.org/10.1111/gwat.12958 - Hopkins, J (2007), “The Cloaca Maxima and the Monumental Manipulation of Water in Archaic Rome” Online: https://waters.iath.virginia.edu/Journal4Hopkins.pdf
- Istat (2024), “Istat Water Statistics – Years 2020-2023”,
*Istat*, https://ngwa.onlinelibrary.wiley.com/doi/pdfdirect/10.1111/gwat.12958