Why The Engineering Behind The Colosseum Was So Advanced | Colosseum: The Story | Unearthed History

Building the Colosseum was the culmination of the career of Emperor Vespasian, and what he built still stands 2,000 years later. Today, one of Italy's noted industrialists has stepped in to preserve it for future generations. Workers are busy scrubbing the grime off the white travertine façade, which is only now starting to divulge many new secrets. Dawn rises on the Colosseum under restoration. Men and women are already at work cleaning the façade. The view from the highest point gives a unique perspective on the engineering of how the world's largest amphitheatre was constructed. Travertine is extremely resistant to water and has provided support for the rest of the Colosseum's structure for 2,000 years. The job entrusted to Conti and her team is not only to restore the ancient glory of the stonework, but also to ensure it has remained impermeable and, where it is fractured, make it waterproof once again. With a resin hammer or with the wooden handle, we check the whole surface to see if the fragments are in situ, stable. We do it using percussion and sound, like a doctor listening to lungs, but also using tactile sensations, because when we put our hand on the stone, we can feel the difference in the vibrations and the extent of any detachments. Over the centuries, various kinds of materials have been used to repair the Colosseum. Today, restorers are using stucco made of a mix of limestone and marble powder, which they have determined will best match the ancient stone. We don't use travertine powder, which would have been coherent as an idea, because aesthetically, travertine powder creates an opaque paste when dried, so we use marble powder. Now I will show you the dried powder, and you can see a variety of the colours we use, so that the workers have a range of hues to arrive at the same colour as the limestone. The stone changes colour naturally over time, so cleaning it also means not destroying the natural colour of the original, which has been subject to weathering. Every step needs to be monitored, so as to avoid turning the monument into an unnaturally white colour. Cleaning between the stones is delicate and time-consuming. This layer that seems to have some tonal discontinuity in the ivory white of the travertine represents, however, the passage of time. It is like my grey hairs from my black hairs, it is an aesthetic choice. I can dye my hair, I can also dye the hair of the Colosseum. We have to allow the visitor to understand that time has passed. The patient and laborious work of cleaning and restoring the facade of the Colosseum is barely the beginning of the massive renovation project, just as getting the travertine stone to Rome was just the first step in building the biggest arena of the Roman Empire. They used the large depression caused by the lake to build the foundation, which was an enormous structure, an elliptical structure with a central space, a sort of donut-shaped foundation layer 13 metres wide. In all, it took 10 years for Vespasian and his sons, Titus and Domitian, to build the massive arena, which was called the Flavian Amphitheatre, after their family name. Although Vespasian died just two years before the massive job was done, this great Roman general's legacy has survived to this day. It was absolutely a short time if you think about the square metres of structure built, and considering the tools and equipment that they had access to. Once inside the Colosseum, engineers used the existing inclined planes inside the cavia to haul slabs of travertine to the highest parts. While slaves did much of the heavy lifting, experts believe specialised artisans were overseeing the work. You can have slaves that can be employed as stone carvers or whatnot for something specific and technical, but it just wasn't convenient for the state to have slaves or employ slaves for this kind of activity. The work, the building of Rome, is done by soldiers, is done by associations and groups of carpenters and masons and so forth, that could have slaves. But again, this is not a city that's built by slaves. Four different companies are believed to have been contracted to build the Colosseum, working simultaneously on different segments. Architects have studied the joints where the different construction companies' segments came together. And inside the monument itself, we see different engineering solutions applied to the same problem. The goal was to build this giant building as fast as possible, not to make it particularly elegant or beautiful. They believe the work was divided in sectors and given to different construction companies that worked at the same time. In various points, we see these joints. There are several places where the arches are deformed, with their heads at different heights. And you can see that this is where the different teams came together. Roman engineering had already performed the miracles of the aqueducts and the Roman roads. And although no designs of the Colosseum have emerged, the basic principles of Roman architecture had been codified. The arch was introduced by the Etruscans, but the Romans understood its potential and used it everywhere, such as in aqueducts and bridges. The arch is a great structure because, with a small amount of material, you can cover large spaces. The arch works because it creates a horizontal force between the blocks that is compensated for when they touch the ground. The strength of crossed arches was already known to the Romans. There were two kinds of arches involved in the Flavian amphitheatre. The barrel vault, made of Roman concrete and bricks, which was built using wooden moulds, and the crossed arch in travertine stone. The distribution of forces gave these arches incredible strength, especially when supported by adjacent arches. Roman concrete was more resistant than its modern equivalent, because its component parts solidified when wet. The arches, the concrete and the travertine all worked together to make the Colosseum extremely solid. In the Colosseum, the horizontal forces that each arch creates is compensated for by the next arch down, so every arch compensates the forces generated by the neighbouring arch. The building was held together thanks to geometry. These huge columns are made of great blocks of stone, and the interplay of arches keeps the whole structure standing. The solid structure that has survived to this day is not only the result of the advanced Roman engineering techniques, but also shows signs of their very practical application to speed up the building work. For 2,000 years, the Colosseum has defied the ravages of time to remain standing. But it won't last forever without regular maintenance and key structural repairs, which are finally being carried out today, thanks to a unique public-private partnership for its restoration. The construction techniques used for the Colosseum are the same as those used in Capua and Verona. The internal surface of the building is covered in brickwork, which functions as a lining for the stone structure, adding uniformity, support and lightness. From this viewpoint you see the exterior grand height of the Colosseum, which has disappeared on the side. It's been damaged by an earthquake, that material's been carted off. We get a view into the interior ring, also of travertine stone, but then it peters out and becomes brick. That's been reconstructed. So when you look at the Colosseum, you're getting all kinds of different views into the history and the reconstruction, the shoring up and the stripping out of this grand monument. This is where one construction segment meets another. The difference in the stonework is clear to the naked eye. The Romans were very pragmatic. They paid attention to detail only where it could be seen. Wherever there were places that couldn't be seen or wouldn't be noticed in the overall building, they didn't spend too much, because precision has a cost. The interior of the Colosseum is different. It's not travertine stone, it's the brickwork, but the brickwork is clad in marble. So the marble veneer has all but disappeared, but you can imagine the entire interior space shining with marble. The top of the Colosseum is still visible today, and you can see a lot of the stonework, it's placed, it looks a little, not quite so neat. From the exterior of it, of course, it's perfectly carved and wonderful and well organized. But on the inside, it wasn't going to be on view, that particular arrangement of the stone blocks, so that cut to the perfection that they could have done. No one's going to see that part, so who cares? We see it today, exposed, and we ask questions. The inside arches betray the junction of the segments. The way the barrel vaults are built can be seen clearly here. The brickwork would have been supported by wooden moulds that held the bricks and mortar together until dry. The construction of amphitheatres, not only of the Colosseum but of all theatres and amphitheatres, was made possible by the massive use of Roman cement, concrete that allowed the Romans to build barrel vaults in series, such as those you can see in the amphitheatres. The stones were laid one on the other without cement, so the masonry had to be extremely precise. Today, when you go inside, it's been partially reconstructed. Now there's even the idea to reconstruct all of it, to allow more access to explore and experience the Colosseum. But in ancient times, it's all wood. And then you have the trapdoors and up top the protagonists, the gladiators and many of the wild animals. Historians believe the format for Roman games involved animal hunts in the morning, executions of criminals at midday, and gladiatorial combats or recreations of famous battles in the afternoon and evening. The big stone structures down below in the foundations held up the lighter structures above, where the public sat to watch the games. As the arches rose upwards, the construction materials used were lighter and lighter. The Colosseum is held up by travertine stone, which are the travertine columns. And it becomes lighter as the structure rises to the upper floors. So the heaviest part is the first level, because it holds up the whole of the upper floors that right now are missing. The entire amphitheater was richly decorated in marble and bronze, with statues in every arch. The whole Colosseum was capped with a sail-like awning to shelter the spectators from the sun. It was held up by ropes and poles resting on ledges all around the construction, each with its own drain to stop the wood rotting in the rain. It can't fall inwards because the radial walls resist inward horizontal pressure, while forces that are pushing outwards are more problematic because there are no outer structures. That's why the Colosseum is not cylindrical but slightly conical and gets narrower towards the top, and this means that the centre of gravity of the stone masses are displaced inwards, and this makes outward collapse more difficult. This is where the less affluent people of Rome would watch the battles in the arena. But even then, they would still be no further than 60 metres from the combat. In 80 AD, the Emperor Titus inaugurated the great arena, with lavish inaugural games and feasting that lasted more than 100 days. Exotic animals were transported from the wilds of Africa for special hunts, and the best fighters were called into service as entertainment. Weeks, months of continuous games, thousands of animals killed, hundreds of men to fight in that arena. But there is one story in particular of two gladiators who get called out of retirement to come back and fight for this big event, a bit like if we were to inaugurate a stadium today, if we were to call back Pele and Backenbauer. At the time of Titus' inaugural games, the cellars were built of wood, not of brickwork. They were made of wood so that they could be dismantled, the arena stage taken down for sea battles and then rebuilt for the gladiatorial combat and the animal hunts. The games that would go down in history as the most lavish, however, were those held by Trajan when he celebrated the conquest of Dacia, today's Romania. The most spectacular games were Trajan's celebration of the conquest of Dacia, which lasted 120 days and over 25,000 gladiators fought each other. The Colossus statue of Nero was preserved, and Hadrian had it moved from near his palace to a place by the amphitheater. It was the Romans' memory of that massive sun-god statue that gave the Flavian amphitheater its nickname, the Colosseum. Just off to the left where you see a couple of little cypress trees, there stood the Colossus. It was an enormous statue. We're talking about the size of the Statue of Liberty, except for the arm was not upraised. It was resting on a pillar. Over time, when we hear of it no more, authors start to call the Flavian amphitheater the Colosseum. The last use of the Colosseum that we know of comes after an edict by Honorius in 404 A.D. And here too, let's remember that there is no perfect recipe for a good gladiator, for a good amphitheater, for the beautiful battle. We are talking about a practice that began in the 3rd century B.C. and that ended at the end of the 5th century A.D., an incredibly long space of time. In a Colosseum that the sources tell us was already partially buried by the events of time, battered by earthquakes, fires and lightning, and the removal of marble. In 528 A.D., at the time of the Longobards in Rome, a hunt is organized. This hunt in 528, in the Colosseum, was the last recorded event of its kind. As Rome declined, the Colosseum was put to many uses. As here at the Theater of Marcellus, houses were built inside the structure. But they did not stay for long. The Colosseum was rich in resources, which over the years would be pillaged and reused in other ways. If you look at the stone on the exterior, you see the travertine blocks oftentimes have holes in them. And those holes tell the tale of people in the Middle Ages extracting the metal pins that were originally joining one block to another block. So in the end, this large abandoned site is becoming a quarry. It's becoming a free shopping mall. People are coming and taking material that they can use again. The molten lead that held the stone blocks together was hacked out. Travertine was burned in lime kilns to make mortar. The urine of horses stabled there eroded the stone for use as saltpeter and gunpowder. Worse was to come. When we look at the exterior of the Colosseum, we don't see that massive 50 meter high exterior around the entire structure. It only exists on one side. What about the other side? What happened? A massive earthquake. And a large section here on one side tumbles down in the middle of the 14th century. So by the time we get into great documented periods like the Renaissance, we read about cartloads of material being taken from this job site or this ruinous site over to St. Peter's facade, hospitals, bridges. Palazzo Venezia was built for the Cardinals of Venice in the 1500s with stones from the Colosseum. They were also used for the lodger of the city of Rome's cathedral, San Giovanni in Laterano, as well as today's French embassy, Palazzo Farnese. Finally, the Colosseum was saved when Pope Benedict XIV declared it a monument to Christian martyrs. No one could touch it any longer. Although coal fires and traffic quickly covered the white facade with a soft black layer of soot. The goal of this work site is not only to take away the deposit of black soot, but also identify all the cracks and create a single map. This has never been done. There's a difference between a small crack at this height and a long crack that goes up to the top. We have to see if it goes all the way up. The layer of black grime led previous restorers to use dark cement to fill in the holes and cracks in the facade. Dr. Conti must renovate the renovations of the past. Much of the stucco laid in those years, the 1950s and 60s, is black. Not because the restorers of the time were incompetent or colorblind, but simply because we have to imagine that the surface was black. They returned the color and integrated the stone with black filling, the color of the stone and its dirty surroundings. The world's most famous monument is not only getting a clean-up, but is also due to be modernized inside and out, amid a storm of controversy. Restorers are hard at work with nebulizers, brushes and sponges, cleaning away the grime of centuries. Renovation is due to take two years. And the problems that face the ancient amphitheater, before it can be fully opened to the public, are still many. Doing conservation work on a site like the Colosseum is going to be multifaceted. It's not just one issue. You've got to always worry about water infiltration. Here on this hillside, overlooking the Colosseum, you see what happens over time, is that water is going to run off, and that runoff can eventually lead to a collapse. Occasionally, you'll have seismic activity, you'll have the threat of earthquakes, so you have ongoing threats. And of course, you have traffic, you have pollution, but you also have a metro line passing underneath, you have the cars and the metro that are creating more seismic activity. Naturally, the vibrations of the heavy traffic, or the irregularity of the frequency of the vibrations, can produce problems for the surface, only if the surface is already weakened. Some of the most advanced monitoring of water infiltration and seismic activity inside an ancient Roman arena is already being done in Verona, to the north. Here, the Romans had designed every seat, every stair, so that water would run off into a complex system of drains. The Romans had designed the seats very differently, in that the way the seat was carved reduced the points of contact, and at the edges, there was a small protuberance carved into the stone to stop water filtering under it. But when the later engineers in Verona replaced the damaged marble seating, they left gaps that allow water to seep through. This situation was not respected when replacing the material, and consequently, from this kind of placement, we have serious problems today. The water infiltrates and goes and damages the arches, threatening to erode the material. We are only filling up the larger cavities, that threaten to let rainwater through the stone facade, into the area of the barrel vaults, which are the true weak point of the monument, that need to be protected from water and vibrations. Any damage to the Roman mortar that holds up the barrel vaults poses a mortal threat to the whole structure. There is no longer a roof on the Colosseum, so the water enters, but we try to maintain the floors below, that are the roof of the arches that are beneath. Aside from the fact that the walls are made of stone, as we turned on the tap to wash, we also stuck a surgical tube in every hole, to see if it went through. The delicate work of gently hammering the stone, to find empty spaces, is time-consuming. Once identified, the hole behind the facade has to be filled up with marble stucco, to make sure water does not filter through to the vaults and further damage them, as they remain the structure on which the whole of the Colosseum still stands. The stucco done here, as you can see, has a different colour tone from the ones we saw before, because it is getting close to the true amber colour of the travertine. Once the job of consolidating the Colosseum is completed, the next step will be to decide what to do with it. The city of Verona has more than a century of experience, using its arena for modern events. They have struck a balance for making necessary repairs to the monument, while making healthy returns for the city. The Verona opera season is an important source of revenue for the whole city. We're talking about 450 million euros of turnover associated with all the activities of the foundation. But most stage managers aren't accustomed to holding events in a structure 2,000 years old. City and government officials are responsible for preserving the monument and also protecting the spectators. Our experience acquired over the years is that the organisers of events born for stadium environments are not flexible in adapting them to archaeological sites, such as the arena. Indeed, over the years, the whole of the arena, almost as large as the Colosseum, has been rendered safe and functional using sensors like this, placed in cracks in the vault under the public seating to register the slightest movement. The system set in place is the most advanced of its kind. Monitoring the structure is done through instruments set up in the arena aimed at verifying the static and dynamic behaviour of the amphitheatre. Just a few days after the system became operational, the city of Verona experienced an earthquake registering 5 on the Richter scale. To his delight, the team were able to verify the mathematical models used to build his system. The earthquake was quite large but did not damage the structure of the arena. Later, his team were able to verify the effects of rock concerts in the arena and reassure the culture ministry that this precious monument was safe. There was a doubt that the sound levels could create problems with the structure, but with this system we could see that in any situation the level of disturbance, such as from the sound levels during the concerts, was in any case smaller than that registered in the earthquake. In a rare visit to the tunnels under the cavia, Mr. Menon illustrates how the Verona arena worked. We don't have traces of how the animals and scenography were put onto the stage, but we know that this space did have two semicircular niches where there was a lift and pulley system. Today, this system of cables and rods keeps the floor stable under the orchestra pit, making the arena suitable for concerts. So far, the Colosseum has not reaped the benefits of show business, but one day the Colosseum cavia could be covered too and concerts and events held there. The new floor could be used for cultural initiatives, so this could give the monument a greater value to the public, enrich its use and its relationship with the public. In fact, whole new areas of the Colosseum that were not accessible to the public before are going to be opened for tours after renovation is complete. The total renovation of the cellars will allow us to open them to visitors, which will be limited to small groups because it is a labyrinth-like structure that requires a guide. As the rest of Rome gets a facelift thanks to private money, restoring and using the Holy Grail of Roman monuments for marketing and promotion is subject to controversy. I think private companies get the fame, but the recognition, it's getting publicity. So, tods, tods, tods, you hear this over and over again because of what they're doing in association with the Colosseum. The Colosseum Restoration Accord calls for not just restoration, but also other initiatives, such as the establishment of a non-profit organization, Friends of the Colosseum, which will operate the external aspects such as managing the monument. The agreement on the Colosseum allows for the creation of a non-profit organization called Friends of the Colosseum, and this association has actually been created to help the spread of cultural activities around the Colosseum. Friends of this organization, Friends of the Colosseum, Friends of the Louvre, and so on, and they're recognized as individuals and as organizations because they too want to help preserve this world heritage. It's not easy. We're going to build a help center that will take out the activities that are at present inside the monument that aren't really compatible with the monument, such as a small bookshop, the ticket office, and toilets. Clearly, we can't create large enough spaces within the monument, while outside the monument we will have more space to help the visitors that we know are at least between five and a half million and six million a year. Diego Dallavalle is the CEO of Tod's Group, an Italian manufacturer of shoes and leather goods who has long been tempted to enter the political arena. The maverick shoemaker struck a deal with the Italian Culture Ministry that allows him to use the Colosseum as a marketing tool. However, he denies any such intention and indeed thinks more private entrepreneurs should be trying to help the Italian state at this difficult time. I would advise my friends, the Italian entrepreneurs, if they haven't already thought about it, to take a minute to think about what they can do for this country, because if we do things as entrepreneurs, it has a practical effect because things get done. The sponsor, who in this case is Dallavalle, or whoever else it might be, wouldn't have been able to give more, doesn't necessarily have to give more, because what is made available is the cost of the work to be done. It doesn't have to cover the entire monument. Nobody gave away the Colosseum in terms of image or property to anyone. Of course, the Colosseum remains the property of the state of Italy. Nothing has been sold. And private sponsorship doesn't take over the protection and monitoring and so on of the Colosseum. The ultimate decision and the ultimate control remains in the hands of the Ministry of Culture and the superintendencies. As long as that happens and you have the transparency so people know where the funds are going, I think it's a win-win situation for everybody. One thing everyone can agree on, however, is the pressing need to preserve what is perhaps the most iconic and haunting image of ancient Rome. The Colosseum is one of the wonders of the ancient world and still stands 2,000 years after it was built. Amphitheatres like this one were venues for gladiatorial entertainment in every Roman city of the empire. There were no less than 230 in the four corners of the Roman world. Rome's Colosseum is the largest arena still standing today. But it is in need of imminent repairs. Man and nature have eroded vast portions of the monument, though it still attracts millions of admirers every year. Restorers are diligently cleaning and consolidating the ancient arena, taking care not to destroy the marks of history. Beneath the floor of the Roman arena was the empire's most powerful propaganda machine, the equipment used for stunning visual effects that wowed the public over and over. The Colosseum's underground cellars represent the emperor's machine for illusions. Obviously the scenery was impressive, just as the shows which were given to the citizens by the emperors to maintain or to increase their popularity were spectacular. The challenges of opening this maze of tunnels and niches to the public, however, are enormous. Before restoring the cellars of the arena, a lot of work needs to be done, above all draining the waters. We must never forget that there's a river that runs under the Colosseum and the water floods the Colosseum when it rains heavily. The controversy surrounding the private funding of urgent restoration work on the monument has opened a whole new discussion on how Italy manages its cultural heritage. All our clients, when they buy our products, somehow they also contribute to the renovation of the Colosseum. Private sponsorship is not the solution, it is a solution, and it's a great solution, but there are so many other things that need to happen and can happen. Hopefully, with this private sponsorship, it's jump-starting the conversation, getting more people involved, more levels of participation involved. That's what I'd like to see. Italy holds three quarters of the world's great works of art, and yet, in the throes of economic crisis, the Italian state is expected to maintain this cultural heritage of the whole of humanity alone. In such a difficult moment for our country, for the whole world economy, but also in Italy, I'd say that the situation we see is very worrying, and we hope it will pass. Well, in moments like this, the most famous people, the strongest companies, I think they should place themselves at their country's disposal. They should do what they can, and they should do it without asking for anything back. The message is, what can we do for our country today? Across Italy, major monuments in need of repair are being restored with the help of discreetly branded sponsorship. The iconic Trevi Fountain, made famous in the Fellini film La Dolce Vita, is today covered in scaffolding, and workers are chipping away at calcium deposits to reveal the original sculptures. Again, a major fashion house made the restoration possible. The Colosseum is no different, say those who support the initiative. If you maintain it, if you invest in it, if you shore it up, because it does need help, this won't stand here forever on its own, you will have something that can be around as long as, you know, humans are around. But you need that investment, you need that care, and the Colosseum is finally getting it. Given the sheer breadth of Italy's cultural heritage and the dire need of protecting it for future generations, a new law was passed in 2004 allowing for several new types of public-private partnerships. In actual fact, the role of the private comes in two forms, either via a donation or via a sponsorship. Surely the sponsorship of the Colosseum is one of the best examples of this. If every big Italian brand adopts a monument, very soon there could be renovation work all over the country, lightening the load on the staff of the cultural ministry. The question is how far the sponsors will be allowed to go to recover the investment in global communication. As far as the cultural ministry is concerned, the issue is simple. What will it cost to get the job done? The entrepreneur Della Valle, the sponsor, contributed a sum of 25 million euros, which is the sum needed to carry out all the work that had to be done to save the façade of the monument, to create a welcome centre and to do the work inside the monument. It was budgeted at 25 million euros, so what the sponsor offered is exactly the sum that needs to be spent to do the work. What I would like is to be recognised as having shown that the time has come to stand up and work for our country and not complain. Restoring one of the wonders of the world is no small feat, but it is not the first time the Colosseum has been restored or rebranded, and probably won't be the last. The restorer is like a doctor and serves society to maintain the monument memento over time, and this gives enormous satisfaction. Never forget the prophecy of the Venerable Bede, an English monk who said, ''As long as the Colosseum stands, Rome will stand. ''When the Colosseum falls, Rome will fall, ''and when Rome falls, so will the world.'' The whole story of the world's most famous stage is a constant work in progress, an ongoing saga of epic proportions.