By Alexis Arevalo-Perez, 11/1/22
All images taken by the author unless otherwise noted
Figure 1: Aqua Claudia and Aqua Anio Novus in Parco degli Aquedotti, the Park of the Aqueducts
Introduction – Aqueducts in the Eternal City
In the early history of Rome, people got their water either from groundwater or directly from the Tiber River. This was noted by Sextus Julius Frontinus in Aqueducts of Rome: “For four hundred and forty-one years from the foundation of the City, the Romans were satisfied with the use of such waters as they drew from the Tiber, from wells, or from springs” (Frontinus et al., 1925). Even as Rome grew large, wells and cisterns remained important sources of drinking water (Deming, 2019). It was only as Rome grew massive that the Empire began to look outward for more water. Aqueducts that brought in clean water from the hills and mountains surrounding the city were the answer.
The history of aqueduct building in Rome spans about 500 years from the building of the Aqua Appia in 312 BCE to the Aqua Alexandrina in 226 CE. In all, the Empire ended up building 11 aqueducts into the city. It was around the time of Julius Caesar, Augustus, and those directly after that the most aqueducts were built. During this time, the following aqueducts were built: “Julia (33 BCE), Virgo (22-19 BCE), Alsietina (2 BCE), Aqua Claudia and Anio Novus (completed in 52 CE), (and) Aqua Traiana (109 CE)” (Cartwright 2021).
In this article, I will follow the journey of Roman aqueduct water from the source to the final terminus locations. The structures along the way will also be covered such as dams, collecting basins, tunnels, arcades, and more. I will also go into the construction techniques and tools used to make the aqueducts, along with some of the major components of aqueducts. Finally, I will talk about the impact of Roman aqueducts and their legacy in modern Rome. My main reason for choosing this topic was because I got to see the main parts of aqueducts during my trip to Italy and was fascinated by the Roman’s engineering feats. My inspirations included the tunnels at Vicovaro, arcades in Parco degli Aquedotti, and fountains throughout the city of Rome.
Journey from the Mountains and Hills
Roman aqueducts began at the source. This could be a spring, river, or a lake. For springs, water was caught in a catchment basin, while rivers and lakes had water diverted through dams. One such catchment basin is shown below in Figure 2.
Figure 2: Water collecting basin for spring water aqueducts (Schram, van Opstal and Passchier)
Frontinus notes the Aqua Appia as originating in the Lucullan estate (Frontinus et al., 1925), Aqua Marcia as beginning “on the Sublacensian Way… at the thirty-eighth milestone, within 200 paces to the left [a view of its source may be seen]. Its waters stand like a tranquil pool, of deep green hue” (Frontinus et al., 1925). These locations are in the mountains east of Rome as shown in the map below. This is the same area that all but one of Rome’s aqueducts got their water from.
Figure 3: A map of some of Rome’s aqueducts and the path they took (Baiocchi, 2020)
From here, most of the journey happened away from sight in tunnels. This originally served a defensive role as underground aqueducts are hidden and easy to defend (NOVA Online | Secrets of Lost Empires | Roman Bath | Watering Ancient Rome). There was also the ease of construction aspect of tunnels as they could be built to follow the contour of the mountainous terrain that aqueduct sources were in. However, tunnels had their limits. As water continued down from the mountains in a tunnel, there would eventually be natural obstacles such as valleys and canyons. Arcades were one way of crossing natural obstacles while keeping a steady slope. Inverted siphons were another option that was used. From beginning to end, a Roman aqueduct could look like the diagram below.
Figure 4: A cross section of a Roman Aqueduct (Todaro, 2020)
Once the water got to Rome, the main length of the aqueduct was completed. At this point, it was now time to distribute the water. The water had to pass through castella, calixes, fountains, baths, toilets, and various other places that Romans used water. Castellum were tanks where water supply was managed. When water dropped below certain levels, certain uses of water began to get cut off. Private homes were the first to go, followed by baths, and finally public fountains. The way they work is presented in Figure 5. Calixes were also used in the distribution of water, being lead pipes that could have their flow changed by a water authority.
Figure 5: Diagram of the castellum at Pompeii (Index of /im/re/Pompeii)
Construction and Tools
The Romans used a technique for tunneling an aqueduct called Eupalino’s technique. This was in order to ensure both tunneling teams would meet when making a tunnel. The idea was that one team started on one side of a mountain and the other would start on the opposite side. This can be seen below in Figure 6. The reason for the use of this technique was to make sure the two tunneling teams would meet in the X-Y plane. Here is how it worked: the teams would tunnel to where they believed the halfway point of the tunnel would be. Once there, one of the teams would tunnel right and the other would go left. Although this means one of the teams would miss and make a tunnel to nowhere, the other teams would make contact. Throughout this whole process, shafts were dug to the surface in order to provide easy access and air. In order to ensure that the shafts were perfectly vertical, a plum bob was hung down from the top. If it was centered, the shaft was straight. This same plum bob was also used to measure the depth of the hole (Cartwright, 2018). This was known as the qanat technique, with the tunnels being known as qanat tunnels. The qanat shafts allowed for maintenance after the construction of the aqueduct. Here is more information if you would like to learn more about this technique: https://www.worldhistory.org/qanat/
Figure 6: Eupalino’s technique drawing from a top-down perspective
In order to determine the starting elevations when using Eupalino’s technique, a tool known as a chorobates was used. One is shown below in Figure 7. This tool functioned like a level but on a larger scale. Bags hung from the left and right side and would only line up with the marks in the chorobates if the ground was level. There was also a trough of water on top that would be used for extra precision on the measurement. Using a perfectly level chorobates and a tall measuring stick at the end position, Roman engineers were able to determine the difference in height between the starting position and the end position. This was done by looking across the surface of the chorobates at the measuring stick and marking that height on the stick. Next, they subtracted the height of the chorobates. Finally, they determined the height difference between the ground level of the stick and the bottom of the chorobates and used geometry to determine how to dig. The team at the higher elevation could then dig down at a constant slope while the lower team dug up at a constant slope. Here is a video of one in action in order to get a better idea of how they worked.
Figure 7: A chorobates, a tool used by Romans (Roman Surveying)
The construction of an arcade involved a ton of planning and effort. Sometimes, as with the Aqua Claudia and Aqua Anio Novus, it was seen as more convenient to stack two aqueducts on each other. This can be seen in the drawing above. Another thing that can be seen is the crane used to lift up the stones into place, with each stone having indents to facilitate the process. Most of the manual labor was done by slaves (How Did Romans Build Aqueducts?), including the quarrying of stones from nearby sources. It is the wide availability of building resources for arcades that made them a viable way to cross canyons and valleys. Arches were built with the help of a wooden support structure. With the help of a chorobates, Roman engineers were able to keep the slope of an aqueduct steady. A tool known as a groma was also used to ensure that sections of the arcade that were supposed to be straight were straight. A groma was used by setting it up along the line that the arcade was supposed to follow. By looking down the groma and putting stakes along the line of sight of one of the groma’s beam, a straight line of stakes could be created. This tool was also used to lay out city grids as the groma is cross shaped.
Figure 8: A drawing of the building of an aqueduct arcade (How Did Romans Build Aqueducts?)
Figure 9: A groma in use (THE AMAZING EVOLUTION OF EARTHMOVING CONSTRUCTION, Part 1 — ECI Technologies, 2020)
To recap, Roman aqueduct tunnels were built with a combination of Eupalino’s technique and the qanat technique. With the help of tools such as the chorobates, they were able to maintain a constant gradient throughout the bore. The groma was another tool used to insure straight lines over long distances.
Tunnels were the backbone of Roman Aqueducts. They made up 80 percent of the total length of all aqueducts (Roman aqueducts: Longest Arcades in Roman aqueducts), making them by far the majority of an aqueduct. They tended to follow the contour of the natural landscape, but occasionally went straight through mountains. These tunnels are short enough that crouching or walking with your head down is required in order to get around. Only in certain areas such as maintenance shaft and some tall sections do the tunnels get high enough to comfortable stand in. The tunnel pictured below in Figure 10 is the Aqua Claudia at Vicovaro.
Figure 10: A section of Aqua Claudia tunnel
Boring the hole was only part of the problem of making an aqueduct tunnel. Next, it had to be lined with concrete to make it impervious. This was done using Roman concrete. This substance was made out of pozzolan, a volcanic ash common to the area around Rome. The same type of concrete was also used to build arcades, roads, bridges, and other structures and was known for its ability to set underwater (Cartwright, 2018).
Figure 11: A section of broken wall lining. Notice the materials inside of the concrete
Figure 12: Water lines inside of an aqueduct tunnel
When an aqueduct tunnel had to be repaired, one option was to send the water in the aqueduct that was going to be repaired into another aqueduct. One example of this is the Aqua Claudia and Aqua Marcia. When the Aqua Claudia underwent repairs, its water was diverted into the Aqua Marcia. In order to handle the greater amount of water, the Aqua Marcia was made larger where it was used as a bypass. Another aspect of tunnel repair was maintenance shafts, which were built during the initial tunneling of the aqueducts for ease of access. One such shaft is shown below.
Figure 13: Maintenance shaft at Vicovaro
Figure 14: The interior of the Aqua Claudia, with fragments of the Aqua Anio Novus resting on top
When people imagine Roman Aqueducts, the first thing that comes to mind is sweeping arcades across the Italian countryside. These arcades were a key aspect of the water delivery system of the Romans, being one of the main ways they crossed natural obstacles to maintain a steady slope in the aqueduct. They are undeniably a critical piece of Roman infrastructure and allowed Rome to prosper. However, they were a small percentage of the overall length of an aqueduct.
The main structure of an arcade consists of multiple arches placed in series next to each other, hence the name arcade. The aqueduct, or aqueducts as in the case of the Aqua Claudia and Aqua Anio Novus, are then placed on top of this structure. The basic structure of a Roman arcade includes the imposts of the arches, the keystone, and the voussoirs. The average slope for the Aqua Claudia was 1.79%, which was around the desired slope of 2% (Baiocchi, 2020).
Figure 15: Roman arch diagram (Arches)
Figure 16: The Aqua Claudia and Aqua Anio Novus
Figure 17: Aqua Claudia/Aqua Anio Novus foundation beneath on of the columns
Figure 18: Column stone with indent in the Aqua Claudia/Aqua Anio Novus arcade.
Figure 19: An indent in a stone on the Aqua Claudia/Aqua Anio Novus arcade. This was used as a grip for a crane during construction
Figure 20: An alternative to indents in the stone, some were lifted by lobes left during the quarrying process
The primary construction materials for an arcade were stones, concrete, and brick. The stones were usually volcanic tuff. As for the concrete, it was made out of pozzolan. This gave it the ability to set underwater. This was also the same concrete that was used to line the tunnels shown earlier.
The Impact of the Aqueducts
The glory of Rome was only possible because of the water provided by the aqueducts that fed its thirst. They allowed for ample drinking water, lavish fountains, public baths, and made spectacles like mock naval battles in artificial lakes possible (Deming, 2019). With the help of all this water, Rome was able to reach a peak population of over one million people (Encyclopedia Britannica).
This tradition of ample drinking water continues on to this day. Around Rome and all of Italy, drinking water fountains known as nasoni spew clean and cold water continuously. Some, as with the nasoni at the Pantheon, even have a bowl for animals to drink out of.
Figure 21: Nasoni in Piazza del Biscione
Figure 22: A nasoni in Florence. Interestingly, this is one of the few I ran into that did not release water constantly, instead needing to be activated with the knob on the right side
Decorative fountains are also prevalent all around the city. Famous examples include Trevi Fountain, Fontana dei Quattro Fiumi in Piazza Navona, Fontana della Barcaccia at the Spanish Steps, and Fontana del Pantheon.
Figure 23: Trevi Fountain
Figure 24: Fontana dei Quattro Fiumi in Piazza Navona
Figure 25: Fontana della Barcaccia at the Spanish Steps
Figure 26: Fontana del Pantheon and the Pantheon. Animal bowls can also be seen in the nasoni in the bottom right corner.
Long after the Fall of Rome, Pope Sixtus V went to work restoring old Roman aqueducts. Called the Aqua Felice (the Pope’s real name was Felice Peretti), this aqueduct can be seen in the Parco degli Aquedotti alongside the Aqua Claudia/Aqua Anio Novus. It ends in the Fontana dell’Acqua Felice, also known as the Fountain of Moses in Rome.
Figure 27: Aqua Felice arcade in the Parco degli Aquedotti
What the future will bring to Rome is anyone’s guess. But one thing is for sure: it will be a future that will echo the past. Whether this is with widely available water, fountains, or arcades, history will continue on.
Figure 28: Fontana di Nettuno in Villa d’Este, a continuation of the Roman fountain tradition
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