Origin and Use of Roman Engineering



Figure 1: Map of the Roman Empire at its greatest extent under Trajan


By Marissa Gelms / 12.04.2015
University of Washington

Introduction

The Roman Empire began in the 8th century BCE rising to power and becoming the most powerful and influential body up until about the 5th century CE (Hammond and Devlin, 2001). Over the years as their empire grew they conquered more and more colonies and with them expanded and built on an ever growing supply of knowledge (figure 1). The Romans were powerful and well respected by those that they conquered largely due to their vast knowledge of engineering and how they used it to make buildings with a purpose (Szasz). “As the Roman Empire expanded to engulf not only the Mediterranean region but also large areas of Western Europe, Roman architects struggled to achieve two overriding aims: to demonstrate the grandeur and power of Rome, while also improving the life of their fellow citizens” (Roman Architecture: Characteristics, Building Techniques). Roman architecture cannot be characterized as just one style since it developed and changed over time becoming several different styles. The Romans mastered a lot of engineering techniques, but the one I am going to focus on in this paper is the arch. It began with the arch, but grew into something so much more powerful and indicative of Roman engineering.

The arch is the foundation of Roman architecture. Where it can almost be said that everything begins and ends with the arch (figures 2, 3, 4, 5, 6, 7). When you think of the pivotal component of Roman engineering the first thing that comes to mind is the arch. The arch has a long history and takes on many forms. The Romans manipulate it in all sorts of ways using it as structure to emblazoning it as it’s own piece of architecture to everything in between. The Romans were so successful at engineering the arch that it is often times one of the things most copied from them. One can not walk the streets of Rome without seeing an arch in one form or another. Without seeing the lasting impression the arch beholds. “In the arch, and the vault that grew out of it, the Romans had a means of thrusting the massive Colosseum walls story above story, of covering a luxurious bathing hall that could accommodate three thousand persons, and of creating the majestic form of the Pantheon” ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍(Roman Architecture: Characteristics, Building Techniques).

   

[LEFT]: Figure 2: A relieving arch on the streets of Rome
[CENTER]: Figure 3: The traditional Roman “true” arch, semicircular
[RIGHT]: Figure 4: Use of different arches at the Baths of Caracalla

   

[LEFT]: Figure 5: Use of semicircular as well as lintel arches at Ostia Antica
[CENTER]: Figure 6: Segmented arch in Ostia Antica
[RIGHT]: Figure 7: Semicircular and pointed arches used in the wall and an arched bridge to the right in Venice.

Origin

Influences

Before Rome became an empire, the city itself developed between the 8th and 4th centuries BCE looking to the Etruscans and Greeks as influences (Roman Architecture: Characteristics, Building Techniques). While the Romans were innovative, they were smart enough to take advantage of the knowledge and resources already available to them. Instead of starting from scratch they developed the already successful technology of the places they had conquered. “Roman architects absorbed a great deal from Etruscan art and design, and had huge respect for both Greek architecture and Greek sculpture. They also learned from Egyptian pyramid architecture and stonework” (Roman Architecture: Characteristics, Building Techniques). While Romans may not have excelled in the arts, often times commissioning artists and using unused scraps of architecture from conquered colonies to decorate their buildings, they did excel in structural engineering making some of the strongest and long-lasting structures known. Often times this structure was built on the concept of the arch.

The Romans by no means invented the arch, as it was around and being used well before there time by the Mesopotamians, however, they were the first to master it and use it to its full potential. The arch dates back to the 2nd millennium BCE and the Romans began using it as early as the sixth century BCE (Ulrich and Quenemoen, 2013). It was from the Etruscans that the Romans learned the techniques for the arch. They practiced and honed their arch making skills for years, using it in every piece of architecture imaginable. They had found something that worked for them and had expanded its use to vaults and domes.

Significance of the Curve

When it came to their architecture the Romans were concerned about ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍”shaping spaces rather than filling the‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍m”(Taylor, 2006, p56). They engineered the arch to be the focal point and used it to flow a structure to the next element. They were faced with being able to bridge space while still emphasizing enclosure. Romans were very observant and keen on using space. Throughout the design they always thought about space and how they could manipulate it. “Interior space, as opposed to structure, is conceived as the prime stuff, with which the designer consciously worked, structure, as merely the means of bounding or articulating space, light, as the means of shaping it” (Brown, 1961). This idea of creating space while still having closure is what the Romans began to build their concept of the curve on. It can then be seen how the arch was a symbol of power because it accomplished what the Romans were looking for. This further leads to the significance that the dome and vault have. Arches made it possible to create more open space and larger doors and windows, ultimately allowing large amounts of light and air into buildings. The use of vaults allowed for less interior supports and thus uninterrupted interior space.

Structural Advantages

The Romans built on their basic knowledge of the arch and learned to use its structural properties to their advantage. The basic structural properties of the arch are that it requires the forces in neighboring stones to work in compression and not in tension. Further, the arch is shaped how it is in order to direct forces outward making it possible to have an open area below it (Ulrich and Quenemoen, 2013)(figure 8). The arch is very powerful and versatile because by simply having large enough vouissers and solid supports one arch could hold many different magnitudes of loads. An important element of Roman technology was speed, as the empire was continuously building new things. The arch is perfect for this since by design it doesn’t require as much wall to be filled in with material. This means less material, less time for construction, less labor, and less cost (Taylor, 2006).

Figure 8: Shows the flow path of the forces acting on an arch

Before the advent of vaulting, in order to create an open and airy feeling the Romans relied on the method of ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍post and lintel (figure 9)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍. In simplest terms this just refers to two vertical posts with a horizontal beam on top that connects them. They have been around for a long time and date back to prehistoric times when it was used in (Ulrich and Quenemoen, 2013). Wood was often used for post and lintel structures because it was light and capable of spanning a large distance. The true need for the arch became apparent when the large spaces of area the Roman’s wanted could no longer be made possible through the use of post and lintel.

Figure 9: Post and Lintel system used frequently before the arch

“Arches and barrel vaults are entirely compressive, while semicircular domes are fully compressive in their upper areas and circumferentially tensile in the lower” (Taylor, 2006 p180). Due to vaulted construction, areas could be made much larger because it was almost all in compression. However, when a material like stone was used, which is heavy, it pushed both downward and outward on the supports requiring a large dead weight in order to counteract it. Thus, unlike post and lintel, walls and piers have to be much thicker for vaulted construction (Fazio, Moffett, and Wodehouse, 2009).

To counteract the lateral thrusts in arches and vaults the Romans came up with some ideas besides just putting multiple arches side by side. They thought of the ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍buttressing arch‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ (figure 10) which is basically just creating huge, heavy walls to support the arch (Lancaster, 2012). Since the walls would be so heavy they would be able to take the lateral thrusts and thus the arch or vault wouldn’t fall. Another way to control the thrusts was to have structural reinforcing in the form of iron tie bars. This solution appeared in the early second century CE in the Baths of Trajan. An anchor block would be attached to the concrete wall and then an iron tie bar would be attached and pass through the crown of the arches so as not to be seen (Lancaster, 2012).‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Come the fourth century, there was a shift towards using exposed tie bars which came about due to changing aesthetic values and that the Romans no longer had access to the materials they normally used to cover up the tie bars (Lancaster, 2012). Being aware of these lateral thrusts and finding ways to counteract them was an important objective for the Romans as their architecture continued to grow in size and their original preventive methods were no longer as feasible.

Figure 10: Use of buttressing arches at the Basilica of Maxentius. Note the huge, thick walls between neighboring arches allowing for the use of less arches.

Types of Arches

There are many different types of arches (figure 12). One of the first types was the corbelled arch which is very different from what the Romans ended up using. It is based on the concept of a cantilever and looks like a bunch of steps where each successive stone is placed a little closer in. These corbelled arches were seen used most often in the passageways of the Mycenae and in Giza for the pyramids (Fazio, Moffett, and Wodehouse, 2009). From the corbelled arch grew the true arch, also known as the semicircular arch (figure 13). It was this arch that the Romans exploited in their architecture. Unlike the corbelled arch, the true arch relies on mutual pressure to stay standing and makes use of a keystone at the top of the arch to keep all the stones together and the arch from falling apart. Without the keystone there would be nothing counteracting the forces so it would collapse. Often times this type of arch will have an odd number of vouissers so that there are an equal amount on either side of the keystone (Arch Construction, 1987). The system of forces acting on each other and keystone was so effective that mortar would not be used to keep the arch standing (Roman Architecture: Characteristics, Building Techniques). The true arch also allowed for longer spans which made it possible to have free space below the arch not possible with the use of the corbelled arch (Fazio, Moffett, and Wodehouse, 2009). As stated before having free space was a quality the Romans were looking for in their architecture. While the semicircular arch was what the Romans excelled at and used most often it didn’t always fit their needs so they developed the flat, lintel arch. “They used the radiating joints to create a flat arch that effectively acted as a beam that was totally in compression” (Ulrich and Quenemoen, 2013 p183). Often times it was used alongside post and lintel structure so as to transfer weight towards the two posts and away from the horizontal, lintel, beam (figure 14). Another type of arch that was often used was the segmented arch which instead of being 180 degrees of a circle, like the semicircular, it is just a segment of a circle with each vouisser having the same radius from the center point (Arch Construction, 1987). This type of arch can be seen most often when used as a relieving arch (see below for more info).

 

[LEFT]: Figure 11: Parts of an arch. Refer to as needed.
[RIGHT]: Figure 12: Different types of arches

 

[LEFT]: Figure 13: Comparing two types of arches. (a)corbelled arch; (b) true arch
[RIGHT]: Figure 14: Lintel arch at Ostia Antica

Construction

Materials

There are three materials that were widely used by the Romans when building arches: stone, concrete, and brick.

Stone

The use of the arch so early on may be due to the availability of volcanic tuff. A material that has much lower tensile strength than other materials making it ideal for use in arches (Ulrich and Quenemoen, 2013). It was also advantageous because it was easy to carve and was resistant to fires. Stone, in general, was a widely used material across the Roman empire that continued to be used throughout the imperial period. It was a powerful material, but took skill and engineering to use. The Romans manipulated and used stone in their own way while still keeping the classical and Hellenistic tradition of it. Once concrete was developed, stone and concrete worked together in Roman design and led to changes in how buildings were approached. In the first and second centuries Roman architecture changed so that the focus was put on the building itself. For this architectural phase concrete was the go to material, but stone followed behind (figure 15). However, stone was a heavy material to work with and thus it also had its ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍restrictions‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍. As stone had to be brought from quarry’s located far distances away it would be difficult to transport this heavy material. A lot more work and labor had to be put into building a stone arch rather than a concrete one which you could just place the formwork and pour.

Figure 15: Stone used in the construction of an arch.

Concrete

An important development in the use of the arch came when the Romans perfected concrete (figure 16). The Romans developed concrete in the 1st century CE from a volcanic ash called pozzolana, which they typically called “pit sand”. Concrete hardened to a stone-like consistency while providing strength and flexibility at a lower cost compared to other materials. It was able to make curves and irregular shapes much easier than other materials and thus was much more convenient to build arches, vaults, and domes (Roman Architecture: Characteristics, Building Techniques). The Romans were no longer restricted to the use of just stone and brick, but were able to create new designs due to the ability of concrete to form to whatever one may want. “[It was] free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick” (Roman Architecture: Characteristics, Building Techniques). The Romans took complete advantage of concrete’s structural abilities. You are not able to change the weight of a material like brick or stone, however, with concrete, builders could change the size of aggregates as the arch or vault was built so that the heavier stone is at the base and lighter stone is at the top. This causes less weight to bear down on the structure making it easier to stay standing (Taylor, 2006). Concrete has so many advantages to other materials and became so widely used in Roman architecture that it may be the reason why many structures have stayed standing today (Roman Architecture: Characteristics, Building Techniques). While concrete became very beneficial to Roman construction it didn’t result in a very appealing finished product so the Romans became skilled at adding finishing to concrete structures such as tiles and marble.

Figure 16: Inner concrete form with facing removed on the via Appia Antica

Brick

While there were arches made completely out of brick, it was more commonly used as a ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍facing ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍for concrete (figure 17). As a facing material it would act as the formwork then you could pour cheap concrete inside and when it is all set you will have a more expensive, better looking exterior. “Over time and distance the Romans used a number of different facing materials and techniques for their concrete buildings, but all shared certain properties” (Taylor, 2006 p97). Facings would be made of small, easily movable materials and essentially served as a mold for concrete to be placed in. This meant that wooden formwork would not be needed. Additionally, facings created a sort of cage making a better curing environment for the concrete by keeping moisture in. This was especially true for brick facing (opus latericium) versus other facing materials which is likely why it was used more often. On a side note, all of these facing techniques made it possible to turn something structurally stable into something also aesthetically appealing. This technique of brick facing was used at least from the Augustan Period (27 BCE-14 CE) onward. The Romans knew that when horizontal bricks were placed so that they overlapped each other they were more resistant to tensile stresses. So they built on this idea with the facing. They hoped that if there was a good enough bond between the core and facing then the resistance caused by placing the bricks like this would transmit to the concrete core. This wasn’t easily accomplished with horizontal bricks, but rather cone and triangular shaped (Taylor, 2006)(figures 18 and 19). From an engineering standpoint this makes sense since these two shapes allow for brick pieces to stick further into the concrete and thus allow for a stronger hold, more cohesion, and less separation.

   

[LEFT]: Figure 17: Brick faced concrete from Ostia Antica. As seen there is only brick lining the perimeter of the structure and the middle is filled with concrete.
[CENTER]: Figure 18: Cone shaped brick used as facing
[RIGHT]: Figure 19: Triangular, wedge shaped brick. As seen it sticks further into concrete core.

Centering

The construction of the semicircular arch relies heavily on the use of centering or scaffolding in order to create the correct form. This formwork is necessary for both stone and concrete arches in order to support the tons of weight (Ulrich and Quenemoen, 2013). We know that centering was a technique used throughout Roman construction as evidence remains in the ruins today. There are many holes in the sides of buildings that suggests that these were used to hold beams to support platforms needed for scaffolding (figure 20 and 21). Further evidence is that on arches still standing today projecting stones can be seen in the arch. These projecting stones is where the formwork for the arch would have rested and are convenient for when any repair work on the arch must be done. The Romans perfected a technique known as flying centering, “a kind of formwork erected not from the ground up but from the springing points of the planned arches or vaults” (Taylor, 2006 p179). Before the centering process would occur it is believed that arches may have been put together on the ground to make sure everything had its appropriate spot and fit together before being fully erected. This is due to the fact that on some existing arch structures today a numbering system can be seen on the vouissers (Ulrich and Quenemoen, 2013). Scaffolding would stay in place until the full construction of the arch was finished as it served as scaffolding for the decorators to use later on. Centering would be made to support only one set of vouissers for an arch or vault at a time so the framework would need to be moved however many times in order to complete the structure, it was most likely moved with the help of ropes. Something builders would have had to think about with centering was the moving of it thus lightness was probably key. While it may be thought that only one centering form would be used and then just moved, this didn’t make sense economically. “Speed and the demands for structural equilibrium required that many vaults be built concurrently” (Taylor, 2006 p182).‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ A key component of centering and thus arches and vaults was the easing process which allowed the centering to drop away from the structure while still keeping it in place to be used for decorators. This process allowed for builders to test the structural stability of the arch or vault to see if it would fail without having to take all of the centering down. It also made it easier for full removal of the centering later on (Taylor, 2006).‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The use of concrete created many problems for centering. First, when building domes it was difficult to create the smooth curved surfaces. Secondly, concrete would stick to the wooden forms which wouldn’t be good when it came time to take the forms down because it is possible that the forms might not come off at all. Builders during the imperial period solved this by placing a layer or two of bricks on the surface of the centering, essentially creating a barricade between the form of the centering and the concrete. Further, concrete was difficult to use with centering because any deformities in the form would directly transfer to whatever was being built and this usually resulted in a flattening of the structure. However, concrete was useful because it allowed builders to work in layers. They could create the formwork and then put a layer of concrete which would slowly harden as new layers were added. As these bottom layers harden less weight will be put on that portion of the formwork and as the concrete slowly continues to strengthen, the higher parts will now take more of the burden.

Centering techniques changed depending on what was being built. A dome’s centering is designed so it can be constructed in layers, radially around itself. Also, since domes have the compression ring at the top, their formwork doesn’t need to span across or prop the crown and thus less formwork is needed. This is not possible, however, for barrel vault centering which needs to be supported below the crown and have beams spanning horizontally across the arch in order to prevent inward collapse. Relieving arches relied on centering constructed through the entire thickness of a wall and set on a flat platform connecting the two walls being spanned by the arch. When successive arches or vaulting is built, due to their thin walls, centering and construction on both arches and vaults must occur concurrently since if only one was done at a time the dividing wall would be put out of balance with the horizontal thrusts and wouldn’t be able to hold.

 

[LEFT]: Figure 20: There are many small, square-like holes in the sides of ruins suggesting they were used to hold scaffolding.
[RIGHT]: Figure 21: Modern day scaffolding being used to make repairs to this arched structure part of Aqua Claudia.

Bonding Courses

Bonding courses are a very distinctive element used from the Flavian period (69 CE-96 CE) until the late third century. Bonding courses seem to serve many purposes. They create a barrier to separate new layers of concrete by placing a layer or two of some material across the entire building surface (figure 22). Subsequently, by creating this barricade it allows for the concrete below it to seal and cure by helping keep all the moisture in. Further, bonding courses created a stable, straight, and level surface on which future layers could be built as well as what scaffolding could be placed on. Both were very crucial to how future arches and vaults could be built and was something they relied on. While these may be beneficial, structurally the only use for a bonding course is that it may add compreseive strength. Thus, “like travertine, brick bonding courses often appear at the springings of arches and vaults” (Taylor, 2006 p104).

Figure 22: Brick bonding courses that separate layers of concrete.

How the Arch was Used

Relieving Arches

“The arches are meant to serve as load-umbrellas, deflecting downward thrusts to either side of a vulnerable spot beneath them, usually a void in a wall” (Taylor, 2006 p109). These are often used for thin walls where there is a concern that the forces may need to be distributed differently. So you would basically have something that looks like an arch, but there would be no void under it and is instead just all wall. Often times this arch was used in multiples by stacking 2 or 3 on top of each other. Each subsequent arch taking part of the load. This type of arch could be seen as a safety precaution, but it most likely served the very real purpose of reducing loads on the post-lintel structure at the top of an opening to something that the structure could actually support. In order for the arch to work properly it had to physically be separated from the wall. In Rome it was common to build new buildings on top of old ones‍‍‍‍‍‍‍‍‍‍. When this type of construction would be done it was common to have relieving arches in order to channel loads to certain points in order to avoid different settling patterns (Lancaster, 2012). ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍There was no formula for how to build relieving arches and they eventually disappeared as a building form over the third century. One example is in the exterior wall of the Pantheon, where 3 levels of relieving arches can be seen (figure 23).

Figure 23: Relieving arch in the side of the Pantheon wall. There is no voided area, but an arch is used to redirect forces.

Aqueducts

Aqueducts were the city’s way of carrying clean water from the mountains and springs down to the city to be used as drinking water and in fountains. In order to keep the water at a constant flow, the aqueduct needed to continually decrease in elevation, but only ever so slightly. Where aqueducts had to cross valley’s, the Romans used arched structures in order to keep the water supply elevated. This part of the aqueduct was just an arcade of arches, one after the other. An excellent example of a surviving aqueduct and how the Romans used their knowledge throughout the empire is the ‍‍‍‍‍Pont du Gard in Nim‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍es, France which makes use of three tiers of arches. On one of our site visits we saw both the Aqua Claudia and Anio Novus which are stacked on top of each other. However, as we had seen aqueducts can be easily broken. Since aqueducts are just made up of a series of arches this allows for the wall between subsequent arches to be thinner than normal because each arch is taking part of the horizontal thrust. This means that if one arch fails it is very likely that a domino effect will occur and multiple arches will begin to fail as the horizontal thrusts are no longer being equally counteracted. This effect was seen at the aquedotti park as out in the field there would just be a lone two arches standing with nothing on either side because they had all fallen (figure 24). Further, at an aqueduct located near the Colosseum only part of the aqueduct remains standing and reinforcing bars can be seen attached to the structure as a means to keep the rest of it standing (figure 25). The bar is there to help counteract the thrust by the missing arches to the left.

 

[LEFT]: Figure 24: Two arches standing alone because they have fallen from the aqueduct.
[RIGHT]: Figure 25: Part of an aqueduct being reinforced with a metal bar so that it doesn’t collapse.

Bridges

Bridges were an essential component of expanding the Roman empire as it allowed for colonies in the farthest reaches of the empire to be connected to each other. The arch was an important element of making the Roman bridge possible (figure 26). In order for an arch to stay standing it is important that it has good supports. Often times when architects built bridges they would take advantage of the best location on a site for pier footings. This often lead to arch spans not being the same size (Taylor, 2006). Both people and automobiles still rely on these arched bridges today with several of them connecting one side of the Tiber to the other.

Figure 26: Arched bridge crossing over the Tiber River.

Vaults

The Romans built on the concept of the arch and innovated the vault. The vault essentially just makes use of the arch form and just extends it creating a system of connected arches. Vaults were originally used for utilitarian structures such as the Cloaca Maxima which by the mid-first century BCE was vaulted with stone.

Structurally, if a wall supported vaults of “roughly equal span and height on both sides, it was allowed to be thinner, since the two vaults would counteract each other’s outward thrusts” (Taylor, 2006 p42). At the Baths of Caracalla this meant that wall thickness could be 1/10 of the span of the vault on that wall. ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍”A vault always wants to flatten and expand horizontally, that is, become more like a straight line”‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ (Taylor, 2006 p43). This is due to the lateral forces acting on the top sidewalls of the vault and pushing outward as well as the weight of the structure from above bearing down on the vault. The combination of these forces causes a vault to want to straighten, but the only thing stopping it are the reaction forces of the walls on either side of the vault pushing back.

There was no way to measure the thickness of vaults which may have led to two common Roman practices. The thickening of the vault toward the bottom and then adding aggregate to the mortar to essentially create a form of concrete making it possible to partially mold the vault into the desired shape. Still, measuring thickness was a problem so when brick ribs began to be used in the construction of concrete vaults in the 3rd century they helped serve as thickness gauges (Taylor, 2006).

The Romans made use of two types of vaults: Barrel and Groin (figure 27). Barrel vaults were ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍just linear ‍‍‍‍‍extensions of the arch. They were used most commonly as a form of vaulted roof. ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍The Colosseum exemplifies the use of the barrel vault‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ (figure 28). From the barrel vault grew the groin vault which is just two barrel vaults that intersect at right angles to each other (Roman Architecture: Characteristics, Building Techniques). It was developed based on the need for something capable of supporting larger loads and being able to span wider areas something that the old post and lintel system was incapable of completing (Roman Architecture: Characteristics, Building Techniques).

 

[LEFT]: Figure 27: Both groin and barrel vaults can be seen along the roof of this Christian Church.
[RIGHT]: Figure 28: Use of barrel vaults in the hallways of the Colosseum.

Dome

The dome is essentially an arch rotated around a center point 360 degrees, “…a group of arches conjoined radially around a vertical axis” (Taylor, 2006 p55) (figure 29). The dome was a huge development because it made it possible to have roofing that would allow for huge open areas that weren’t hindered by beams or columns since they weren’t needed for support. Some iconic buildings that ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍make use of the dome include the Pantheon and the Basilica of Constantine. Often times dome’s are made from concrete because their weight can easily be manipulated. Remarkably, the Pantheon is still the ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍largest non-reinforced concrete dome in the world (Roman Architecture: Characteristics, Building Techniques). The upper part of the vault was made lighter so not as much force was being bared down on the structure (Ulrich and Quenemoen, 2013). Domes were often dark not allowing much light in, but the Romans used their knowledge of structure to fix this by creating an oculus, a round hole at the top of a dome. The addition of this oculus is essentially the removal of the keystone in a series of arches, but “the dome’s advantage [of] circumferential or hoop stresses” allows there to be a ring of compression that keeps the dome standing (Taylor, 2006 p 55). It is interesting to think about how this hole is actually beneficial to the construction of the dome and in fact acts as a buttress itself.

Figure 29: The famous dome on St. Peter’s Basilica.

Triumphal Arches

These were stand-alone, commemorative arches designed to show the Roman power and be lasting impressions. They were completed by emperors or military leaders who had done something necessary of rememberance, often due to some important event or military campaign (Roman Architecture: Characteristics, Building Techniques). These arches are basically just one large decoration as they aren’t used as support to hold up anything else and they are covered with inscriptions and designs detailing their victories and what they have been erected for. The‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ 3 notable triumphal arches still standing in Rome are the Arch of Constantine, Arch of Titus, and Arch of Septimus Severus (figures 30, 31, and 32). In my opinion the fact that the Romans chose the arch as a means of communicating their victories in battle just goes to show how significant this structure was to them. They have chosen this one piece of engineering that they have entwined in so much architecture to stand alone and speak for itself how much of an impact it made to shaping Roman engineering.

   

[LEFT]: Figure 30: Arch of Constantine
[CENTER]: Figure 31: Arch of Titus
[RIGHT]: Figure 32: Arch of Septimus Severus

Adapting Ideas of Conquered Colonies

As the empire grew, the Roman’s learned to take advantage of the construction methods from the provinces they were conquering. These methods had worked so far for these places so they learned and expanded their supply of knowledge. They adopted and adapted local materials and traditions to fit their new architectural needs.

Greece and Asia Minor

From these provinces the Romans adapted the use of bricks for how they created vaults. “[Vaults] were often built with an intrados (see figure 2) of radially laid bricks (one or two bricks thick) and then mortared rubble was added above to create the vault” (Ulrich and Quenemoen, 2013 p188). The Roman’s took this idea and instead set the bricks vertically and in order to fit the curve of a barrel vault they would be made in trapezoidal forms. “This method of building was probably brought from Parthia after Trajan’s Parthian War…” (Ulrich and Quenemoen, 2013 p188).

Egypt

Unlike Rome who built their arches by setting the bricks radially, the Egyptians built them from pitched mudbrick and set them on edge side by side. Due to this setup mortar was needed to keep bricks attached to one another and so a mixture of mud was used. Another innovation the Egyptians used was to slant their arches which prevented bricks from sliding off and thus made it unnecessary to use centering. “The vaulted rooms were either covered by barrel vaults, which often took a tall parabolic form instead of the more typical segment of a circle, or by vaults springing from all four walls, such as sail vaults, which spring from spherical pendentives, or squinch vaults, which spring from conical forms across the four corners” (Ulrich and Quenemoen, 2013 p189).

North Africa

In North Africa a technique of using terracotta vaulting tubes to build vaults was being used. It appeared around the second century CE. This technique also made it so that external centering wasn’t needed since the tubes themselves acted as centering that the building material could be laid on. Tubes could connect to each other and gypsum mortar was needed in order to keep them connected. “By the fourth century, what had started as a permanent centering for concrete developed into a thin, lightweight vault on its own” (Ulrich and Quenemoen, 2013 p190). This technique is mostly found in Christian churches in Italy.

Europe and Britain

Throughout the rest of Europe and Britain barrel vaults were being created in a very different way. “Ribs were formed of brick voussoirs with tenons extending horizontally from the bottom so that a flat terracotta slab spanned between each pair of ribs” (Ulrich and Quenemoen, 2013 p191).

Influences after the Fall of the Empire

Rome was a powerful and influential empire. Many cultures copied the Romans because they wanted to copy the success and power they had (Hammond and Devlin, 2001). Everything from the bridges to the aqueducts to the roads became models and were influential for architects and engineers everywhere. However, the largest influence on construction in the west would have to be the arch with which the Romans “set the standard for most types of monumental architecture” (Roman Architecture: Characteristics, Building Techniques). They influenced everything from Byzantine art with Hagia Sophia to medieval Russian architecture with the onion domes of St Basil’s Cathedral to Renaissance architecture to Baroque architecture to Neoclassical architecture. Many of the world’s most famous pieces of engineering must give credit to the Roman arch because without it they may not be standing today. “[Architects] such as Filippo Brunelleschi designer of the iconic dome of the cathedral in Florence, and both Donato Bramante and Michelangelo, designers of St Peter’s Basilica” looked to the Romans as guides (Roman Architecture: Characteristics, Building Techniques).

One specific influence can be seen in the triumphal arches which served as models for “fifty generations of triumphant militarists” (Roman Architecture: Characteristics, Building Techniques). The most famous is the Arc de Triomphe in Paris that Napoleon Bonaparte built based off of the Arch of Titus (figure 33). Roman influence can even be seen here in the U.S. with our Capitol building and its dome. The Roman influence knows no bounds. They may have started with something basic, just a semicircular arch, but the arch and vault changed visually through time. There were pointed arches and horseshoe arches then there was rib vaulting and fan vaulting. The arch, vault, and dome changed through time as design and need required it, but it all started with the Romans. “Imitation is the sincerest form of flattery.” The mere fact that so many pieces of architecture through time have looked to the Romans as examples and have used the arch that they mastered goes to show that the Romans must have done something right.

Figure 33: The Arc de Triomphe in Paris based off of the Arch of Titus

As I can attest from my time in Rome, although most decorations no longer remain, it has allowed for Rome’s true masterpiece to be revealed. Most buildings and arches have lost there finishing surfaces leaving the underlying structure visible. This wasn’t something the Romans had planned, but one can truly see the engineering behind it. They accomplished so much and there structural engineering has truly stood the test of time. I see more beauty and accomplishment in any of the plain concrete arched walls still standing today than any decoration could have ever proven. In my opinion no one has been able to reach what the Romans were able to accomplish with the arch.

References

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Brown, Frank Edward. Roman Architecture. New York: G. Braziller, 1961. Print.

Fazio, Michael W., Marian Moffett, and Lawrence Wodehouse. Buildings across Time: An Introduction to World Architecture: ARCH 150/151, Appreciation of Architecture I & II, University of Washington. McGraw Hill, 2009. Print.

Hammond, Aaron, and Thomas Devlin. “Technology in Ancient Rome.” (2001). Web. 5 Sept. 2015. <http://www.scientiareview.org/pdfs/258.pdf>.

Lancaster, Lynne. “Roman Engineering and Construction.” The Oxford Handbook of Cnt,rinecring and Technology (2012). Web. 15 Sept. 2015.

“Roman Architecture (c.400 BCE – 400 CE).” Roman Architecture: Characteristics, Building Techniques. Web. 8 Sept. 2015. <http://www.visual-arts-cork.com/architecture/roman.htm>.

Szasz, Colin. “The Influence of Roman Engineering and Architecture.” Web. 5 Sept. 2015. <http://www.arch.mcgill.ca/prof/sijpkes/arch304/winter2001/cszasz/u1/roman.htm>.

Taylor, Rabun. Roman Builders: A Study in Architectural Process. Cambridge: Cambridge UP, 2006. Print.

Ulrich, Roger Bradley, and Caroline K. Quenemoen. A Companion to Roman Architecture. 1st ed. Wiley-Blackwell, 2013. Web. 8 Sept. 2015.

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