Engineering Rome

Underground Rome and its Influence on Modern Day Construction

by Chloe Coughlan.
Photos are by author unless otherwise stated

1. Introduction

The remains of the Roman empire have for thousands of years created a lasting impression of the innovating engineering and construction abilities used by its citizens. With structures as massive as the Colosseum, the Pantheon, and the Roman Forum, it is hard to downplay the magnitude of power the Roman Empire had at its peak. Though an equal but far less well-known indicator of the Roman’s engineering and construction abilities, the portion of ancient Rome that lies underground has given us clues to parts of the city’s unique history as well as the technical aspects that went into its construction. The scale of Rome’s underground city is impressive not only because of how well it has been preserved, but also for how it affects modern Rome, especially with the type of construction happening there in the past few decades. There is a portion of ancient Rome still in tact, with multiple houses, aqueducts, churches, and mines scattered all over Rome, meters under ground level. This underground ancient world has been the result of a more complex modern city which has been developed by working around these unique barriers. Ancient Rome has been preserved and revealed from careful excavations done by archaeologists and construction teams, though some discoveries have been accidental. Numerous discoveries have been the result of a different type of archaeology in this city. Urban Speleology, a term made more well known by the group ‘Roma Sotterranea’, is the scientific study of man made caves, their structure, physical properties, and history, which leads to a discovery of ruins of great value and importance (Roma Sotterranea). Teams like these make it possible for ancient Rome to continue to be intensely discovered, in turn adding to the history of Rome.

This paper will start off by discussing the history of Ancient Rome and the causes by which its ground level rose and buried parts of the city. This rise in ground level that buried parts of the city are the basis for why modern building is Rome can be so complicated. This paper will then move on to modern implications with construction techniques and the barriers that construction workers have encountered in the past few decades when trying to advance transportation and building construction in Rome.

2. History of Rome

2.1 Geological Setting

The location of the city center of Rome was established based on its proximity to a naturally occurring water source, an abundant resource of building materials from surrounding quarry areas, and opportunities for expansion. Over a number of centuries, the geological evolution of the Tiber valley involved relocations of the Tiber river and flooding of the Valley, which deposited silty clay and sand in the region of the city center (Burghignoli & Callisto, 2013). These environmental evolutions were only the beginning of the changing settings of Rome, which would later be plagued with a series of fires, earthquakes, city wide floods, and reconstructions, which will be discussed in a later section. The geological setting of ancient Rome played an important part in how widely it would affect modern day construction as well as our ability to discover more about it.

2.2 Building Techniques

At Ancient Rome’s peak, the city had about 1.5 million inhabitants (Strickland, 2010). For such a large number of citizens, enough buildings to support them were necessary, and structures had to go up quickly. The building materials of this time period were mostly naturally occurring, and this included stone and timber. Brick and glass were also common manufactured materials, and Roman concrete was also widely used. These resources were available throughout the Roman Empire, which allowed rapid progress and expansion. The two most important buildings materials of the Roman empire were Roman concrete and brick. Roman concrete was made with pozzolan, lime, and water, which even had the ability to cure underwater. These two components essentially formed the majority of Roman structures, which is evident from what we see standing today. The Romans also utilized the natural deposits of travertine and tufa in their area. Travertine is a sedimentary limestone that has the ability to carry heavy loads due to its inherent compression strength. Vitruvius preferred to use travertine, due to its ability to “endure every strain whether it be stress or the injuries inflicted by harsh weather” (Strickland, 2010). The Engineering Rome group had the opportunity to visit a travertine quarry, where the process of cutting, polishing, and transporting the stone was shown. The stone almost has a modern look, and continues to be used decoratively on buildings. Travertine’s popularity is said to have diminished when Augustus favored marble over travertine as a material for adorning building exteriors. Tufa, coming from the tuff mines, is a “porous, solidified volcanic mud, resulting in a somewhat weak stone. It was used primarily for interior construction, such as platforms for temples” (Strickland, 2010).The Romans also utilized wood, which was a simple building material. However, their use of wood is harder to trace, is it was widely destroyed in fires. The combination of the Roman’s clever use of materials combined with their ingenious construction techniques provided a foundation for a city than lasted well beyond the years of the empire, the test of natural disasters, and additional thousands of years. Their structures have been some of the most well known and longest standing in the world, which is what makes the history of Rome so intricate.

Figure 1: Photo by author. Example of materials at the Baths of Caracalla.

2.3 The Great Fire of A.D 64

Though a majority of the history surrounding the Great Fire of 64 AD focuses on Emperor Nero and whether or not he purposely set ablaze to the city of Rome, this paper will be focusing on what came after the fire. This event was a turning point in Ancient Rome because it set a new foundation for the city. The Great Fire of 64 AD burned for almost a week straight and destroyed nearly half of Rome. Because marble, concrete, and other stones were materials that were used primarily by the wealthy, a large portion of the city was made up of wood. The fire left almost three quarters of the city in ruins with little to be salvaged. Soon after this destruction, Emperor Nero took the opportunity to build himself a new palace on top of the area that had been burned. In modern day construction, when a new project is starting, usually the first act is to clear away the debris from what previously vacated the area. This could include demolishing a building, or clearing dirt away from the area in order to build into the ground. After the fire of 64 AD, an enormous amount of debris had been created from singed homes, foliage, and other buildings. Around this same time period, the Tiber River had been plagued with a number of catastrophic floods that brought additional debris and earth matter to the streets of Rome. The combination of debris from the numerous floods and the fire caused the ground level of Rome to rise by a significant number of meters. Though some Romans took the opportunity to build on top of the rising ground, the floods from the Tiber river were worsened by silt deposits which buried a vast number of buildings when the ground level began to rise (Eaton, 2004).

2.4 Rebuilding Rome

The tendency of Ancient Romans to use the debris of old structures while rebuilding after demolition contributed to the geological causes that over time significantly changed the altimetry of Rome. Excavations over the past few centuries have led to discoveries that portions of Ancient Rome were up to 7 to 11 meters under current ground level (Burghignoli & Callisto, 2013). For example, this knowledge is evident in some buildings at The Forum. At the Temple of Antoninus and Faustina, a temple built by emperor Antoninus Pius (A.D. 86-161), the main doorway is significantly higher than the ground level of the fully excavated main square, shown below.

Figure 2: Photo by author. Raised ground level of the Temple of Antoninus and Faustina

Due to the flooding and geographical issues that affected the area, the site of the Forum had previously been a marshy lake where waters from the surrounding hills drained. The combination of the low elevation of the forum, constant flooding of the Tiber, and erosion from nearby hills caused the ground level to steadily rise for centuries. Even in early times the sediment eroded from the hills was raising the ground (Eaton, 2004). The following photograph depicts another example of the outer ruins of the forum at a much higher level than the rest of the square.

Figure 3: Temples of Saturn & Vespasian at a higher level than the rest of the Forum.

2.4.1 San Clemente Basilica

The Basilica of San Clemente, a structure containing evidence of the many layers of Ancient Rome, provides a foundation (literally) to many similar multi-level buildings located all over the city. The basilica provides clues to how the Romans adapted to their rising ground level by reusing building material and spaces, while maintaining the old building structure. The lowest level of San Clemente was built sometime in the 1st century and was originally a combination villa and warehouse, separated only by a small alley in the lowest level (Roma Sotterranea). The lowest levels of the building were thought to have been destroyed in the Great Fire of 64 AD and in order to preserve the foundation, San Clemente was then filled with rubble and debris in order to create a stronger basis where a new level was built upon it. (Sacred Destinations). This same concept was applied to the second level, which was the location of the first of two churches on this spot. This level of the Basilica was not excavated until the beginning of the 19th century, and archaeologists then discovered ancient columns that belonged to the first layer of church. The second Basilica, built in the 12th century, is what visitors see today when they come to time hop between levels of this building (Sacred Destinations).

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Figure 4: The levels of the San Clemente Basilica. Retrieved from:

Though even the newest church at San Clemente is centuries old and does not directly affect modern construction, it has been useful in ways that it has provided clues about the beginning of Italian history, including language, history of Saints, and has given insight into how building materials were reused after the Great Fire. The Basilica of San Clemente is thought to be one of the most well preserved examples of this multi-level building approach. With this model, it becomes easier to understand how other monuments like the Forum and buildings alike have survived the test of time with this unique structure.

More information about the Basilica of San Clemente can be found here.

3. Modern Building Dilemmas

3.1 Metro Line

As the city of Rome continues to grow and develop, new techniques are needed in order to sustain the economic stability that it’s citizens rely on. Transportation is a major development in most large cities, and Rome has adapted by paving new roads, restoring old buildings, and developing an underground public transportation system. Because Rome has such a long and available history that still affects the modern city, transportation is an aspect of construction that has been widely been limited because of this. The underground metro lines are one example of Rome attempting to adapt to modern transportation while still protecting its history.

Currently, the Rome metro system has two lines: A and B, which cross the city of Rome in an ‘X’ shape. The Metro Line C is the newest section of the underground railway system in Rome, which when completed, will stretch from Cloddio-Mazzani to Pantano, intersecting Linea A at the San-Giovanni station. Archeological work site operations began on May 16th, 2006, and two Tunnel Boring Machines were put into place on March 8th, 2007. (Metro C). Metro Linea C’s underground tunnel section consists of two side-by-side circular tunnels which have a diameter of 5.80 meters (19.02 feet) and lie at a depth of between 20 to 35 feet below ground level. Stated on the Metro Line C website, their mission is “to give Rome and its citizens a new functional, efficient, and modern underground line, built with the most advanced construction technologies in the mass transport infrastructure sector in an urban setting.” They also state that their goal is to capitalize on Rome’s heritage that makes it one of the world’s most-visited cities (Metro C). Though the mission of the Metro C can be related to most other public transportation projects in large cities, its obstacles are unique. In addition to its underground treasures, because of the interesting ground level patterns that Rome has dealt with, the soil quality has added to the complications in using the tunnel boring machines. Near the San Giovanni station, the tunnels run mainly into fine-grained Pleistocene and Holocene soils.This Holocene type soil represents how the human species have grown worldwide, including transitioning toward urban living (Burghignoli & Callisto, 2013). Knowing these soil types can provide further clues about how the city of Rome was shaped. In order to construct the two parallel tunnels required for the Metro Line C, a tunnel boring machine is necessary. For tunneling in this type of softer soil, the head of the TBM cuts through the face of soil which is then extracted through a conveyer belt that goes along the shaft of the machine where it is then discharged (Burghignoli & Callisto, 2013). Because the metro line tunnels are so deep, the majority of the evasive work happens when shafts are created for stations or air ventilation. A picture of the Metro Line C tunnel boring machine is shown below.

Figure 5: The side of the tunnel boring machine.
Figure 6: Teeth of the tunnel boring machine.

3.2 Hazard Assessment

Another hazard these engineers have to take into account is how underground tunneling and excavations will affect the surrounding structures. For massive structures such as the coliseum, the self-weight can cause slight damage to the ground over time. “Buildings that are closer to the tunnel axis tend to assume a deformed configuration with an upward concavity (sagging), while buildings that are far from the tunnel axis tend to assume a deformed configuration with a downward concavity (hogging)” (Burghignoli & Callisto, 2013). If the curvature exceeds a certain value, the building may be subject to structural damage to a varying extend. When working underground near extremely old buildings in Rome, engineers have to be sure to be extremely careful of these technicalities.

In addition to the numerous buildings that are hidden beneath Rome’s surface which could contribute to the instability of buildings, another relevant issue for underground Rome are the Tuff mines, abandoned from centuries ago. These mines have potential to pose a safety risk to modern day Rome, and an assessment in 2011 by a number of researchers for the Bulletin of Engineering Geology and the Environment took place. “The tuffs, particularly the Tufo Lionato (meaning ‘Lion Tuff’, for its yellowish color) are an excellent building material used for many monuments while the pozzolana deposits have been used extensively since the Roman era for the production of a kind of concrete” (Bozzano & Cercato, 2011). Though the Romans were praised for their engineering and construction skills, these thousand-year-old underground cavities are destined to encounter some collapses and such, which can in turn cause sudden road collapses, failures of pipelines, and fissures in buildings.

Figure 7: Underground at the abandoned tuff mines.

3.3 Cloaca Maxima

Because so much of modern Rome is the result of construction from centuries ago, the natural tendency of things to begin to break down is inevitable. Another one of Rome’s treasures, though not glamorous at all is the Cloaca Maxima. The Cloaca Maxima, otherwise known as the “Great Sewer” of central Rome, has been around since the sixth century BC, making it one of the oldest surviving structures in Rome’s history. (Bozzano & Cercato, 2011). Though it lacks the grandeur that other attractions such as the Coliseum and Pantheon hold, the Cloaca Maxima is just as important. The Cloaca Maxima runs underground, when at its full expansion included the flow from 11 aqueducts, with an opening at the Roman Forum and disperses into the Tiber River. An opening near the Ponte Rotto bridge in the Trastevere neighborhood shows the mouth of this ancient system, and while still intact, the sewer looks dried up and well out of reach of water level. As old as this sewer is, a majority of its insides are still uncharted. Though the water flow through the Cloaca Maxima is typically no more than a slight trickle, annual flooding of the Tiber river has been prone to cause some backflow up through the sewer tunnels.

In the Byzantine era, the Cloaca Maxima still remained in use, but suffered from severe neglect, along with other important structures in Rome’s ancient central area. Adding to the other uncharted areas of Rome’s hidden underground, the Cloaca Maxima was not thoroughly examined for centuries until 2012, when a robot was sent through the tunnels of the sewer in order to collect data on its status. The Cloaca Maxima was discovered to be extremely fragile, with necessary maintenance on its forecast. A collapse of one part of the sewer would be certain to cause damage to Rome’s city network, affecting the daily lives of many citizens.

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Figure 8: The Cloaca Maxima as seen from the Tiber river
Retrieved from:

4. Underground Discoveries

4.1 Aqua Appia

The metro line C has encountered a number of problems consistent with traditional subway systems, but unique to the city of Rome, the excavations have led to a number of accidental artifact discoveries, including that of one of the oldest aqueducts in Rome, dating from the 3rd century BC. This aqueduct was discovered under the Piazza Celimonatana, and unearthed as 32 meters long, though it is certain to extended in length past both unearthed ends (Sassi, 2017).
At the time of its discovery, the Aqua Appia was the oldest aqueduct discovery in Rome. Construction dated back to 312 BC, where other large aqueducts were centuries newer. The aqueduct laid almost 20 meters deep under the heart of the city, in an area that would never have been uncovered if it hadn’t been for the work on the Rome metro lines. Simona Morretta, the heritage department’s head archeologist, stated “the ruins emerged during work on a ventilation shaft about 32 meters wide and involving an area of about 800 square meters for line C of the metro, which started over two years ago” (Sassi, 2017). Though the discovery of this aqueduct provided a great deal of information to archeologists about additional ways the Romans got their water, it is still unknown where the Aqua Appia started or ended. The aqueduct, built in blocks of gray ‘cappellaccio’ tuff, rose about two meters high, and surely continued both east and west beyond the bulkheads and the diameter of the shaft. Archaeologists have predicted that a public work of this size would have taken decades to build, which adds to its impressive factor. Here is what archaeologists have called “a sensational discovery of enormous importance, because it is almost certainly the most ancient Roman aqueduct, dating from the third century before Christ” (Sassi, 2017). In order to preserve the Aqua Appia, archaeologists concluded that carefully removing the aqueduct from its current location and reassembling it in a space where the public could view it would give new life to the ancient treasure. At 20 meters below ground level, the chances of any citizens ever appreciating it were very low. Adriano Morabito, the founder of Roma Sotterranea, presented a quick synopsis of the process in removing the aqueduct. Each brick of the Aqua Appia was numbered in the order it was assembled, and removed one by one in order to preserve the material while keeping the ability to reassemble the aqueduct in it’s exact form in a different location.

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Figure 9: Discovery of Aqua Appia. Retrieved from:
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Figure 10: Aqua Appia archaeological site. Retrieved from:

The addition of public transportation to Rome’s already complicated web of busses, trams, and trains was certain to hold an insurmountable amount of planning from all types of departments: engineering, construction, archaeology, architecture, and more. In order to add another fully functioning link to Rome’s underground transit system, the unique factors of Rome’s underground needed to be taken into account, which in turn created something of an ethical problem when challenges inevitably arose. Archeological excavations were put into place, and 18 excavations in the T4, T5, T6A, and T7 zones had archeological finds. The finds from these excavations included but were not limited to: an ancient road system, a system of agricultural works, masonry structures from a villa, a type of roman catacombs, construction from the ancient Aqua Alexandrina like mentioned above, a Roman-era furnace, and an Imperial Age-reservoir. The dilemma when archaeological finds revealed Ancient Roman artifacts such as these was whether to remove the artifact and continue with plans, or to change plans completely in order to not disturb the artifacts. Even this step in the process is unlike anything that other modern cities have to deal with, which makes the city of Rome that much more complicated. (Metro C).

Figure 11: Map of Metro Line C. Retrieved from:

4.2 Solution to Archaeological Discoveries

According to its website, the Metro Line C has taken a number of preventative steps to safeguard its monumental and unique heritage. (Metro C). Archaeologists discovered a total of 56 monuments, monumental areas, and historic buildings. To protect these discoveries, the Customer Roma Metropolitane prepared the Line/Monuments Interaction study. “The Line/Monuments interaction study provided sound technical and scientific support for defining the measures to safeguard the monuments, and the corresponding monitoring project.”

For this study the following activities were performed:

  • Reconstructing the buildings’ “architectural history” by means of a broad research campaign at the properties and in the archives, while verifying how the structural interventions performed in the past may have modified their static behaviour;
  • Survey and photographic documentation, with a high degree of detail, of the cracking situation currently present;
  • Defining, by onsite surveys, the types and geometries of the ground structures;
  • Analysing, using the most modern diagnostic survey techniques, the mechanical properties and constitutive bonds of the structural elements and of the materials used for the construction;
  • Constructing complex mathematical models, thanks to special software, capable of faithfully reproducing the historic monument/building;
  • Calculating, based on the design data, the subsidence basins induced by the excavations, and of induced stress situation in correspondence with the structural elements;
  • Designing an adequate monitoring system;
  • Designing safeguarding measures aimed at minimizing the induced effects.

For more information, visit the website.

In order to create a positive social impact from these recent archeological discoveries, engineers working on the Metro Line C at the San Giovanni station settled on creating an immersive experience for passengers with a portion of the artifacts they discovered. The new metro line station could be thought of as more of a museum than a regular station, with hundreds of artifacts lining the walls and floor of the station. These artifacts are displayed in glass cases on the floors, with timelines on the walls, and other displays around the edges of the station. The discoveries date as far back as the Pleistocene age and first century BC, from Imperial Rome to the Middle Ages. Artifacts include iron spearheads, gold coins, bronze fish hooks, woven baskets, and marble statues. During this decade long project, more than 40,000 artifacts have been discovered (Sassi, 2017). Filippo Lambertucci, a professor of archaeology from Rome’s La Sapienza University, spoke about the San Giovanni metro station. “We’ve tried to create an immersive experience for passengers, it sheds light on the daily life of ancient Romans and people living in subsequent centuries” (Sassi, 2017). It is examples like these, where Rome’s ancient underground had the opportunity to immensely affect its modern day construction, where a simple and positive solution can lead to the best results.

external image TELEMMGLPICT000125293582_trans_NvBQzQNjv4Bqek9vKm18v_rkIPH9w2GMNtm3NAjPW-2_OvjCiS6COCU.jpeg?imwidth=1400
Figure 12: San Giovanni metro station. Retrieved from:

5. Benefits of Underground Transportation + Comparison

Though underground transportation is the main construction barrier I have discussed in this paper, there are many others that have affected the progression and modernization of Rome. I will briefly go into detail about the benefits of underground expansion, noting when and if Rome could take advantage of these concepts. Evident from the transportation expansion in Rome, it is clear than many ancient cities with dense urban environments have taken steps in the past few decades to solve problems related to pollution, traffic congestion, and lack of space for work and recreation, by building in more sustainable ways. Improved public transit is an important example. Increasingly common in large urban cities, underground mass transit systems have been shown to offer benefits that widely outnumber road traffic and even above ground public transit. Studies show that car traffic takes up 30 to 90 times more space than metro systems. Similarly, public road transport takes 3 to 12 times more space. Underground transit allows more limited disturbance to above road transportation and offers an environmentally friendly option to daily commutes (Broere, 2015). In addition to transportation solutions, underground infrastructure has been shown to offer better natural protection against environmental elements, including destructive weather and seismic events. Underground facilities and metro systems are less prone to earthquake damage have suffered little or no damage in major earthquakes (Broere, 2015).

I have mentioned numerous times above that Rome is a unique city that has more obstacles to overcome than the average urban environment. Though their need for transportation expansion has been inflated by the massive number of tourists that come to visit yearly, Rome has had to adapt with a modern transportation system and structural elements while maintaining a balance with its worldly and ancient history. Rome may never be able to become as modern as cities like Seattle or Paris because of its underground heritage. For example, The Alaskan Highway in Seattle will be the largest diameter bored tunnel in the world when completed,and a semi-new underground tunnel in Paris in the A86 has the capability for two levels of transit (Broere, 2015). However, engineering and construction capabilities can only strengthen, which may eventually change how we see Rome.

6. Roma Sotterranea

Roma Sotterranea is a non-profit group dedicated to the exploration of the subterranean places beneath Rome and the surrounding areas. The group uses geologists, archaeologists, engineers and more in order to understand past civilizations. By using both invasive and non-invasive techniques, the people of Roma Sotterranea have made it possible for groups to explore the ancient Aqua Claudia, Tuff Mines and ancient Roman houses, as well as have a better understanding of why certain structures in modern day Rome, such as paved roads, suffer due to their past. The mission of Roma Sotterranea is to discover a significant part of the underground environments that make Rome so unique by using data collection and hands on experiences. In this way, they can share the discovery of ruins of great value and importance. “Modern archaeology is a science directly derived from art, history and from an antiquarian mentality. This brought to “discrimination” against works that, although fundamental in the understanding of a past civilization (with its developments and historical evolutions) were deprived of any importance” (Roma Sotterranea). Groups like these bring great value to their community, not only because there is little knowledge about their work, but because it can engage many people with different professions. “With the objective of encouraging a better understanding of the subterranean places, we decided to create a professional figure able to escort and help archaeologists in their underground investigations and research: people whose role is to explore, map, survey, gather archaeologists’ prescribed analyses” (Roma Sotterraenea). Members were able to take the Engineering Rome group on a number of underground adventures to learn about site histories as well as the construction and engineering techniques that went into them. The impressive wealth of knowledge the Roma Sotterranea members boasted provided for a knowledgeable and entertaining experience.

7. Conclusion

Rome is a much more complex city than how it appears. Its grand history is evident, scattered across the city center, and it gets only more impressive with age. However, as our world evolves and becomes more modern, Rome has been faced with difficulties that other cities can not relate to. Underground Rome, just one of the barriers that the city faces with urbanization, is a topic that most citizens have little knowledge about. Through groups like Roma Sotterranea and teams of archaeologists working with engineers and transportation teams, the hidden parts of underground Rome have the potential to lead to amazing discoveries. In conclusion, underground Rome is a part of the city that affects more than what it seems to. The main construction element is transportation and its ability to grow in Rome. The metro line C is a great example of this adaption to urbanization in Rome, and the artifacts which resulted from this construction overall contributed positively to Rome’s society and history. Though there are a number of hazards that go along with construction in such an ancient city, careful planning, engineering, and archaeological discoveries have the opportunity to advance Rome.

8. References

Bozzano, F., Cercato, M., Fasani, G. (2011, Nov). The underground cavity network of southeastern Rome. Bulletin of Engineering Geology and the Environment.

Broere, W. (2015). Urban underground space: Solving the problems of today’s cities. Science Direct, 55, pp.245-248.

Burghignoli, A., Callisto L., Rampello S. (2013). The crossing of the historical centre of Rome by the new underground Line C. Pages 97-136.

Eaton, J. (Sept, 2004). The Forum Romanum. Retrieved from

Metro C. (2017). Metro C S.c.p.A.

Roma Sotterranea. (2017). Roma Sotterranea – Speleology for Archaeology.

Sacred Destinations. San Clemente. (2017).

Sassi, E. (2017, April). Roman Aqueduct Discovered under Piazza Celimontana. Corriere Della Sera.

Strickland, M. (2010, Aug). Roman Building Materials, Construction Methods, and Architecture: The Identity of an Empire. (Graduate Dissertation). Retrieved from

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