By Katie Leija
Photos are by the author unless otherwise stated.
Ancient Rome is known for brutal gladiator fights, winding cobblestone roads, an everlasting government structure, and much more. Above all else, Rome is best known for its monumental architecture of sparkling marble and sturdy concrete. These materials are the most popular, but there still exists an equally important and beautiful material utilized by both Ancient Romans and modern Italians: travertine.
My mother used to be a history teacher, who used historical events as story time. My father is an engineer and still quizzes me on the mechanics of everything from amusement park rides to bicycles. My uncle is a geologist who still brings me new rocks and gems. All of this combined meant that I was raised to obsess over Ancient Rome. Since taking up a Classical Studies minor, I have been able to connect stories I was raised with to more in-depth information and the humanities and society of antiquity to the engineering I study more.
Since arriving in Rome, I have marveled at the ancient buildings around me. My prior education left me wondering about the construction of important monuments like the Colosseum and Pantheon. Further research and trips to these locations brought travertine to my attention. It is a stone much more durable than marble and is often confused for it at first glance, yet I had never heard of it before coming to Rome. Thus I knew that I wanted to know more about it.
In this article, I will explore travertine in Ancient Rome, from its creation in the quarries of Tivoli to its use in monuments like the Colosseum. Specifically, I will explore how the conditions of the Acque Albule Basin led to the unique features of Roman travertine, how the cultural importance of travertine encouraged its use in antiquity, and the methods by which Romans transported the heavy stone.
Creation
Travertine in Ancient Rome was formed and quarried thirty kilometers from the city center in Tivoli, then known as “Tibur.” In antiquity, travertine was called lapis Tiburtinus for the city it came from (Grawehr, 2022). Today, travertine comes in shades of white, gray, yellow, and brown, though in antiquity yellow and white versions of the stone seem to be used more. Figure 1 shows examples of travertine used today, while Figure 2 shows the ancient color used in the Theatre of Marcellus.
Travertine is a sedimentary rock that forms near mineral springs. It is formed when calcium carbonate and organisms such as bacteria and moss precipitate over and over again, forming layers that are 2-8 centimeters high at a time, as seen in the cut below in Figure 3 (Jackson, et al, 2005). The continuous rise and fall of the water in the springs also aids in the unique formation of travertine: erosion of the stone occurs when water levels fall and sediment settles towards the bottom as water rises.
Mountains surround the quarries of Tivoli, ensuring that the Acque Albule Basin (Figure 4) they reside in never runs out of water. The sulfurous nature of the Acque Albule Basin aids in the creation of travertine and gives Roman travertine a unique pale yellow color. I can attest that it also provides the Pacifici Cava in Tivoli with a rotten egg smell. Tivoli travertine is also unique due to the depth of the quarry. At sixty meters deep, the travertine deposits in Tivoli are more compact than those found in Mexico or Spain (Poggi Bros, 2022). The sedimentary and aquatic formation of travertine gives the stone different properties than other common Roman construction materials. In the next section, we will discuss these distinctive characteristics.
Properties
Recording and studying the physical properties of construction materials is not a modern idea. Sometime between 30-20 BCE, the Roman engineer and architect Vitruvius wrote De Architectura, the only surviving ancient treatise on architecture. In his book, he classifies soft, medium, and hard materials and lists travertine (translated as the “Tiburtine stones”) as a medium species. This is interpreted to mean that travertine has a medium maximum compressive strength, smaller than hard stones like basalt at 250 MPa but larger than soft stones like tuff at 45 MPa. Figure 5 shows some of the physical properties of travertine compared to other common Roman construction materials. Carrara marble has a greater compressive strength than travertine (133.4 MPa versus 104.8 MPa), but it is also denser. Conversely, both tuff and Roman concrete are significantly less dense than travertine but also have a significantly smaller compressive strength.
Having felt and collected my own pieces of travertine, I can attest that it does feel like a medium stone, nowhere near as soft as talc or even calcite, but not as hard as granite or quartzite. It lands between a four and five on the Mohs scale of hardness, making it slightly more scratch-resistant than marble at three (Poggi Bros, 2022). Hitting one piece of travertine against another may chip the rocks but it will not completely break either. It can also produce a nice ringing noise reminiscent of a bell, as can be observed in Figure 6.
Possibly the most notable characteristic of travertine is its resistance to weathering. The part water plays in its formation means that the stone has a very low water absorption rate (less than one percent compared to tuff’s 10-27 percent). Soft stones such as tuff have high water absorption rates and thus erode much more due to the elements. Unfortunately, this same feature means that stones that absorb little water are “easily injured by fire,” so travertine structures would have broken down much more than those of tuff in any of the many fires the nation faced (Vitruvius, 2017). Travertine in particular is more prone to fire damage than other medium stones due to its porous structure. The sulfuric nature of the Acque Albule basin causes air bubbles to form in travertine (Figure 7), allowing oxygen to better feed any flames that meet the stone (Poggi Bros, 2022).
The porous nature of travertine also makes it difficult to carve intricate imagery into the stone, especially when compared to Carrara marble, which has similar physical properties. Marble was favored by the Romans for its malleability and glamor, although its location far from the Roman center made it much more expensive. When looking to save money, Ancient Romans instead used travertine with a stucco finish to achieve the stability and luxury they craved (Grawehr, 2022). This remained the status quo largely from the first recorded use of travertine in the Temple of Concord in 121 BCE to possibly 23 BCE, when construction for the Theatre of Marcellus began. Scholars debate over whether or not the theatre’s exterior travertine was covered in stucco. At the moment, there are no traces of stucco on the travertine, making the Theatre of Marcellus the first major building to have significantly exposed travertine.
While exposed travertine became more popular towards the end of the first century BCE, marble was still greatly preferred by the emperors. For Caesar Augustus and his successors, marble, specifically colored marble from outside of Rome, was a symbol of the power the Roman Empire was amassing over its neighbors (Lancaster, Ulrich, 2014). Travertine primarily remained a structural material until the rise of the Flavian dynasty in 69 CE. Hoping to separate themselves from the overindulgent reign of Nero and the tumultuous Year of the Four Emperors, the rulers of the Flavian dynasty preferred travertine over marble. The best-known example of this is the Colosseum, which began construction in 72 CE under Vespasian and was completed in 80 CE under Titus (Grawehr, 2022). Made largely of travertine and Roman concrete, the Colosseum (Figure 8) is now the face of Ancient Rome and represents the stability and frugality the later emperors wished to display.
Quarry
While many travertine quarries are in use today, none have been running as long as the quarries of Tivoli. The travertine deposit was first discovered by the Romans in the third century BCE, although its first known use in construction only dates back to 121 BCE. To this day, travertine is mined from the quarries (Figure 9) and used across the world, but how did the Ancient Romans first get a hold of the stone?
Travertine is typically extracted from a surface quarry as opposed to a cave. Thus, the first step in mining must be to remove the overburden, the layer of earth above the desired stone. If the workers are lucky, then the rocks will have fissures that they can use to extract pieces of stone by using metal or wooden wedges and crowbars (Adams, 1994). More often than not, quarrymen would have to use pickaxes to create these cracks themselves. Figure 10 shows what this site would look like for a surface quarry such as travertine. Figure 11 shows this process in action for a tuff mine. While tuff was mined in caves and holds many different physical properties than travertine, the overall process was still the same for antiquity.
The quarrymen would switch between cutting and marking with a pickaxe and striking the wedge with a mallet as needed until the desired block was mined. Sometimes, the quarrymen would place dry wooden wedges into fissures and then soak them with water. As the now wet wood expanded, it would increase the cracks in the stone and loosen it even more (Adams, 1994). Figure 12 depicts a relief of ancient masonry tools, many of which would be used for quarrying. A pickaxe (center left) and wedges (right) are notably visible.
Quarrymen continued mining from a predetermined section downwards until it became too difficult to lift the stone to the surface. For some materials, the workers moved into/make caves to further mine the material horizontally. While this is true for stones such as tuff, it does not seem to be the case for travertine.
As previously mentioned, tuff is a soft species of stone and is thus easier to carve. Several tuff quarries, such as those under the Temple of Claudius (Figure 13), are man-made caves. Tuff’s malleability makes it possible for quarrymen to carve stable caverns as they mine. Travertine on the other hand is difficult to carve like this. It is also not needed for quarrymen to move horizontally when mining travertine. The quarries of Tivoli began forming more than 100,000 years ago in the Pleistocene geological period and are all around 60 meters deep (Poggi Bros, 2022). Thus, there remains an ample supply of travertine that is easier to access in the open air as opposed to caves. The travertine quarry, while smellier than the tuff quarry, also has the benefit of natural light and a less frightening atmosphere.
The same methods for extracting stone were often used for cutting stone as well. As the quarrymen had hopefully already taken advantage of the fissures of the stone to extract the blocks, they would make new openings for the wedges using a chisel and mallet, as seen in Figure 14. (Adams, 1994). They would then use a pickaxe to make notches between the wedges, creating a line of breakage similar to perforated paper today.
Saws were also commonly used to cut rock, although they were not necessarily more accurate than wedges. While a wedge is a much faster tool, internal fissures not visible from the surface could cause unwanted cracks or cuts in the wrong direction. Using a saw was slower but more precise, so it was often used on more expensive rocks like marble (Adams, 1994). For travertine, a serrated blade would be used and water was poured over it to limit heating.
Next, the cut stone would be roughly dressed using a hammer and punch, a thicker version of a chisel. The stone block would be roughed out into its approximate final shape, making transportation easier and lighter. The worker would then switch to using an actual, precise chisel to refine his work. He may have also polished the stone by wetting the surface and rubbing it with an abrasive rock, just like wet sanding today (Adams, 1994). Sometimes, the final dressing would not occur until the stone reached the construction site, as it may just get roughed up again during transportation. The next section will explore how Ancient Romans transported travertine out of the quarry, as well as to construction sites.
Transportation
As seen in Figure 9, the travertine quarry is incredibly deep, so moving 20-ton blocks of stone requires more than just manpower. If the quarry was not too deep at the time, quarrymen would place the stone blocks on rollers and push them up an access ramp (Figure 15). This method required building a stable ramp and could become obsolete the moment the quarry became too deep.
Luckily for the Romans, the Ancient Greeks had long ago invented machines for heavy lifting (Vitruvius, 2017). These machines were easier to modify to meet the needs of growing quarries. They were largely made out of wood, so they no longer survive today. We know what these machines may have looked like due to archaeological art (Figure 16) and written records. Vitruvius describes one such machine with “Two beams required for the jib, their thickness depending on the maximum probable load…fixed together at the top with an iron bracket, and separated at the base, like an inverted V. Ropes are attached to the head of the jib, and arranged to keep it steady. A pulley block is suspended from the top.”
There were many different types of pulley machines, all of which more or less amount to cranes. They came in many different shapes and sizes, depending on the predicted load being lifted. Other differences include the placements of the pulley blocks, pulley wheels, and winches, as well as the amount of each. Figure 17 depicts another type of pulley crane found in Capua that more closely aligns with Vitruvius’ description than the crane from Figure 16.
After lifting the stone up and out of the quarry using the crane, the workers would then need to remove the ropes. Ideally, the workers could just wrap the ropes under and over the stone blocks, but it would be much too difficult to get the stone off of the ropes. Instead, they had different methods of preparing the blocks beforehand to ease the process. Figure 18 depicts three of these methods: Greek-invented handling bosses and lewises and Roman-invented grips (Adams, 1994).
Handling bosses were pieces of the stone purposely left jutting out during the rough-dressing. The rope would wrap around and under just these pieces as opposed to the whole block. Unfortunately, it added extra work for both the rough and finer dressing. The lewis was a metal configuration that grabbed onto the stone, where a worker would cut a cavity into the top of the stone that was the same size as his lewis and then connect the device through there. Lewises were preferred over handling bosses due to their speed and overall ease. Handling bosses were typically only used over lewises when the top surface of the stone was meant to be used for decoration. Grips were even faster and easier than lewises and required less prep work on the stone. A worker only had to make two symmetrical holes the size of the grip on either side of the block. However, this method placed a limit on the dimensions of the blocks as the grips could only open so wide before they became ineffective. Thus, lewises were still preferred overall (Adams, 1994).
Once the travertine was completely out of the quarry, it had to be transported to the construction site. Part of the reason why Tivoli’s quarry flourished above others is because of its proximity to the Aniene River (Figure 19), which was once connected to the Tiber/Tevere River (Figure 20).
Until 30 BCE, travertine was only transported to Rome via these two rivers. Figure 21 is a map of Tivoli relative to the rivers and Rome. The blocks of stone would be loaded onto wooden rafts on the Aniene River. Some accounts state that the flow of the river would be enough to carry the travertine down the river (Poggi Bros, 2022). Others claim that upon reaching the Tiber River, oars, sails, and even towing in some parts would be necessary to maintain movement (Campbell, 2012). Nonetheless, the boats would have been relatively small and made of wood, so they are not intact today. Like many other minute details of Antiquity, we know that the boats existed due to accounts from Pliny.
Travertine was only transported by land around 30 BCE when the Via Tiburtina, an Ancient Roman road, was cleared for heavy cargo (Grawehr, 2022). The travertine blocks would be placed onto wooden wagons and then pulled by oxen to Rome. Figure 22 depicts an example of a wagon carrying supplies. It is important to note that this wagon is pulled by horses, which would not be able to carry the heavy blocks of travertine.
Upon reaching its destination, the travertine would be lifted onto construction sites and buildings using the pulley crane systems previously mentioned. Figure 16 itself is specifically a depiction of the crane being used on a nearly finished construction site.
Conclusion
While not as well known as marble or concrete, travertine undeniably holds a significant role in both Ancient and modern Roman construction. The unique conditions of the Acque Albule Basin led to Roman travertine developing physical properties, unlike any other stone. Its use in Antiquity is further encouraged by the tumultuous politics of the Roman Empire.
Quarrying and transporting the stone remains a long and challenging process. While methods of mining travertine have developed since Antiquity, they still hold roots in the original techniques of the Romans. Today, companies like Pacifici and the Poggi Bros mine the same quarries as Ancient Romans. They use diamond blade saws instead of chisels and hammers, but they still use water to prevent overheating. Excavators replace pure man power, but cranes are still used throughout the quarrying process.
Travertine’s inclusion in monuments such as the Colosseum, Theatre of Marcellus, Hadrian’s Villa, and many more means that the stone will forever be engraved and remembered in the history of Rome.
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