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00:01Imperial Rome, a modern city in an ancient world.
00:06Over 2,000 years ago, the Romans built a stadium for 50,000 people,
00:13provided clean water for one million, and worshipped in an engineering phenomenon.
00:21All masterminded without electricity, gas, or any of the technology we know today.
00:27So you got 5,200 pounds. You think three people can do it?
00:31Our team of experts is setting out to uncover the secrets of a whole trailblazing city.
00:37This is not a job for archaeologists. These guys are top engineering specialists,
00:43and they're about to step into the shoes of the men who built Rome.
00:57Ancient Rome, still awe-inspiring today, even to the experts.
01:07This team of leading construction specialists wants to investigate, reimagine, and recreate Rome's greatest triumphs
01:15to understand the skill behind the spectacle.
01:18Steve Burrows is an internationally renowned structural engineer.
01:25He's behind some of our great modern monuments, including the centerpiece of the Beijing Olympics.
01:30Just as the Bersnest Stadium is an iconic symbol for the Beijing Olympic Games,
01:35so this stadium was an iconic symbol of rain.
01:38Steve's guide on the journey is Dr. Melinda Hartwig, an expert in the classical world.
01:42The task for architectural designer Charlie Luxton is to decode these buildings from their plans and blueprints.
01:50While 5,000 miles away at the University of Louisiana at Lafayette, Dr. Chris Carroll has set up a field lab.
01:58With his students, his goal is to put the research into practice and demonstrate Roman tricks of the trade.
02:05To see what they did 2,000 years ago, it still stands. It's just remarkable.
02:10One ancient Roman building overshadows all the others.
02:15It still dominates the skyline.
02:18It's 15 stories high and covers an area over four football fields in size.
02:25It's the Colosseum, where crowds came to see the gladiators fight for their lives.
02:31Thousands of people were killed here.
02:35And despite its bloody past, every sporting venue built since owes it a massive debt.
02:46Wow.
02:48Amazing, isn't it?
02:50The first thing that strikes you when you see the Colosseum from the outside is just the scale,
02:54the height of that building above the ground.
02:56It is a massive structure and it's meant to proclaim the wealth and the power of Rome.
03:01The most important thing was keeping the masses happy.
03:05Keep them entertained and this is the way to the hearts of the people.
03:10There's very few buildings that you know exactly what they are and exactly what they do just by looking at the plan.
03:17But the Colosseum is one of them.
03:18Looking at this, you know that it's a stadium.
03:20Yet the design is nearly 2,000 years old.
03:25So what went through the minds of the men who planned and built the Colosseum?
03:31How did they arrive at this design?
03:33After all, their building was the first.
03:37They created the blueprint.
03:39I've been involved in building several large international stadiums and they all have similar problems, similar opportunities too.
03:46It's always been about handling crowds.
03:50Huge numbers of people converging in a single place at a single time.
03:55At the Colosseum, 50,000 spectators.
03:59Large crowds have to get into these buildings very safely and leave very safely.
04:03So the first thing you need to consider in the design of a stadium is how you get people into their seats in a very direct line and safely.
04:10And that's why you have lots of openings in the outside wall of the stadium.
04:12The Colosseum builders have the same concerns.
04:16The ground level has 80 openings.
04:1976 are numbered entrances.
04:22The next consideration is that everybody who gets to their seats has to have a good view of the action.
04:27And that means that you need a seating bowl.
04:29You need this sort of curve shape which creates a triangle for the structure with the heaviest load on the outside.
04:34There's a very clear reason why this design hasn't changed in almost 2,000 years.
04:41It's the only way to make sure everyone can see.
04:45Cut through the stands, there's a triangular cross section.
04:49All the weight is focused down the outside.
04:52And the choice of material is crucial.
04:55In a modern structure, that outside frame is made of steel or reinforced concrete.
05:01But in this case, it's just made of stone.
05:04Imagine building a stone wall 150 feet high, strong enough to carry a serious load, but not so massive that it collapses under its own weight or sinks into the ground below.
05:15That's a challenge in any age.
05:19They could have done it in a number of ways.
05:22One is to have built a solid wall, but that would have been far too heavy, put extra load on the foundations.
05:27How to reduce the load?
05:30Ingeniously simple.
05:32240 holes.
05:34Not round holes, but arches.
05:37A shape you see time and again in Roman construction.
05:41But why?
05:42They're complex to build.
05:45Could the arch be the first clue as to why this building is still standing after 2,000 years?
05:53In his field lab in Lafayette, Louisiana, Chris Carroll and his students are going to find out.
05:59It's time to conduct an experiment.
06:02So we have cast two specimens here.
06:04One is just a typical beam and one is an arch.
06:07Both have the same thickness, the same width, the same concrete with the same strength.
06:10So we're going to go ahead and load these up and see how much they can take.
06:14A beam is easier and quicker to construct than an arch.
06:18But will it bear the same load?
06:21Each of these concrete blocks weighs 1,200 pounds, as much as a small car.
06:27Two down, and it holds.
06:34But at 3,600 pounds, it's catastrophic failure.
06:41This proves that the Coliseum builders couldn't have used beams to span those entrances.
06:46Now for the arch.
06:52All right, go ahead, pull out.
06:54We'll grab two more.
06:56That's four blocks.
06:58Even with six blocks, the weight of a truck bearing down on it, the arch doesn't fail.
07:03This is two times the amount that we used to break our slab.
07:07But the arch, you can see, is still not broken.
07:10So Roman arches were not just for decoration or to be pretty.
07:12You can see that there is a structural purpose to an arch.
07:15The arches reduce the weight of the wall and make it stronger.
07:19But this small-scale experiment just creates more mysteries.
07:23Two thousand years ago, there were no extended boom forklifts like Chris's.
07:30So to build walls like this, how did they even lift the stone?
07:42Today, we have cranes to help build our grandest structures.
07:46But it was a different story in ancient Rome.
07:48So far, the team has decoded the mystery of the Colosseum arches.
07:53But they want to investigate just how the Romans got them this high in the first place.
07:59If we were building this stadium today, we'd use huge quantities of plant and equipment.
08:04The Romans lifted blocks of stone weighing two tons, 170 feet up into the air.
08:10That's the height of a 15-story building.
08:12The mystery for me is just how did they do that?
08:14What equipment did they use?
08:15The best clue may lie a few miles north in the Vatican.
08:21Melinda's brought Steve to look at a carving from an ancient Roman tomb belonging to a family of builders.
08:28The scene reveals an incredible window into the past.
08:32It shows a remarkable device.
08:35This, of course, is one of the machines that they would have used in order to lift very, very large blocks into place.
08:41The principle of it is pretty simple.
08:43These are lifting ropes.
08:46And these are the stays that were used for moving the mast.
08:49The wheel here, this is actually the engine of the machine.
08:52So a few people, at least five people depicted in this scene here, would have been able to lift a huge load by walking around in the wheel like a hamster wheel.
09:00Could this be the secret of how the Coliseum stones were moved?
09:05The tomb dates to the same era, but there are no other images from this time of a machine like this.
09:11Does it work in practice?
09:14There's only one way to find out.
09:16Build one.
09:17In Louisiana, Dr. Chris Carroll has called in the help of David Girard, an expert in building complex wooden machines.
09:26We'll figure it out.
09:28We've built quite a few complicated structures in the past, mostly for the oil field and railroad.
09:33It was quite fun, I have to admit.
09:35After studying the design in the Roman carving, David orders some seriously big timber.
09:42The Romans might have used oxen.
09:45He uses a ten-wheeler truck to carry the pieces under escort to the site.
09:50The scale of the wheel is dictated by the height of a Roman slave.
09:54We figured the wheel had to be at least 14 feet in diameter if a Roman man was standing in it walking without his head hitting.
10:04So the wheel generates the crane's power.
10:08Maintaining the proportions in the carving, you get a boom over 30 feet long.
10:13What we're going to do with the cranes, we're going to have them assemble it here.
10:16This crane is going to operate from a fixed position, but the Romans had to move theirs all the time.
10:22We have an idea of how they would have moved it around, so we think they would have set it on the wheel and rolled it on the wheel and used that as transportation.
10:31To work safely, it will always need anchoring.
10:35Five pylons are hammered six feet into the ground.
10:39The ropes from the boom are wound through blocks and secured.
10:44We went with two triple blocks on either side of the boom.
10:47And those came down to a tie back pollen, so these boom lines actually hold the entire load up when it's suspended.
10:56The crane is now primed and ready for the test.
11:00When you're making a large building like the Colosseum or any of these great Roman structures, there is a huge amount of temporary works that needs to go on.
11:07And all we sort of see is what's left after the construction phase.
11:12But during building, you need scaffolding, you need access ramps and you need lifting devices.
11:18Because when you build a tall building, you have to build something taller to lift that last block or piece onto it, which then goes away and you're left with the perfection of the original design.
11:29But behind that, in these temporary works, is a whole other layer of incredible ingenuity.
11:38Imagine dozens of these surrounding the Roman Colosseum.
11:43Now, this was used to lift the blocks into place.
11:46And one of the key components that allows you to do that is the pulley system.
11:49Now, this pulley system that we have will actually reduce the weight that we're lifting by a factor of eight.
11:54The pulley system, a block and tackle, is one of history's most important, most powerful inventions.
12:02Each time the rope passes through the block, its length is doubled.
12:07This increase in distance decreases the force needed to lift the load.
12:12It is called mechanical advantage.
12:16On the crane, the pulleys make any weight eight times easier to lift.
12:20Now, we can also look at the ratios of the diameter of the wheel and the diameter of the axle.
12:25So, for example, if that ratio is ten, then we would be able to reduce the force we have to pull with by a factor of ten.
12:31The wheel spreads the work out.
12:34Because it is ten times bigger than the axle, each time it turns, it generates ten times the force.
12:41Put it all together, and the crane should make any weight 80 times easier to lift.
12:45Now, the next thing for us is we actually want to get some people in here and see how much we can really lift.
12:51Time for a test drive.
12:53Can it lift the weight of one stone block in the Coliseum?
12:575,200 pounds.
12:59Chris wants a practice run first with just 1,200 pounds.
13:03The Romans used slaves for the grunt work.
13:06Student Rachel stands in.
13:07All right, Rachel, let's go. Start rolling.
13:10Rachel only weighs a tenth of the block's weight.
13:15But with the crane's mechanical advantage, Chris calculates that Rachel can lift it alone.
13:23And she does.
13:25It just feels like I'm running uphill.
13:27She's able to lift a 1,200-pound block with very little effort, like you said, other than just running uphill.
13:32That's all that it takes.
13:33So, the device works.
13:36But how well?
13:38Could it lift a stone in the Coliseum?
13:40Chris wants proof.
13:43It's time for the big lift.
13:46Just over two and a half tons.
13:49All right, so you got 5,200 pounds.
13:51You think three people can do it?
13:52Absolutely.
13:53All right, let's see what you got.
13:54The way the pulley system works, the team is going to have to walk a long way before they see the block move.
14:03Up, up.
14:05What's the stretch in? I can hear it.
14:07The ropes are creaking under the tension.
14:10This is the sound of ancient Roman engineering.
14:22They've been walking now for three minutes.
14:24We've got lift off.
14:30Let's see it.
14:31And two and a half tons have lifted off the ground.
14:34All right, that's good. Hold up right there.
14:38All right, so you got 5,200 pounds four feet off the ground.
14:42How hard was that?
14:44It was a little tough, but considering we did that with just three people.
14:47What do you got a breath for?
14:51It's a success.
14:53Chris's experiment proves the device in the carving really works.
14:58It's an ancient crane, almost certainly used in the Colosseum build.
15:03But as the city of Rome grew, its engineers were presented with a new challenge.
15:09How do you supply a million people with clean, safe drinking water?
15:17The Romans built the largest amphitheater in the ancient world, the Colosseum.
15:27It was the star attraction in the world's biggest city, capital of an empire.
15:33Over a 150-year span, Rome's population almost tripled.
15:38Rome was a modern city in every sense.
15:41There were over a million people that lived in this city.
15:44With a million people, there come a number of problems, the most pressing of which is water.
15:51You really wouldn't choose to build Rome where it is.
15:55There are a number of big problems.
15:57The first is that it sits on seven hills, and there are no major springs or water sources at the top of these hills.
16:04And there is one river, the Tiber.
16:06And that is relied upon for not only all the city's fresh drinking water, but it becomes where all the human waste goes, the garbage, and even dead bodies.
16:17It became horrendously polluted.
16:19So you need another solution.
16:22And this map shows the Roman solution.
16:26Eleven lifelines coming into the city, a network of aqueducts.
16:32A Roman aqueduct is a vast machine, up to 50 miles long.
16:36In the field lab, Dr. Chris Carroll and his team attempt a daunting task.
16:43Transport pure, clean water the Roman way.
16:48They're going to build their own aqueduct.
16:51Same obstacles, same problems, same solutions.
16:55Just a little smaller.
16:57We're going to set up the wall line for the aqueduct, and then we're going to draw on the concrete with pencil where the wall is going to be and make sure everything is plumb.
17:09Even with modern surveying equipment, building an aqueduct is a big job.
17:14Chris's team works into the night.
17:17A little more, dead on.
17:19Yeah, check it again to make sure.
17:21Timber form work will give the structure its shape.
17:25It's got to be precise.
17:26They can only pour the concrete once.
17:29Pretty good.
17:31Not bad at all.
17:33One of the closest clean water sources to Rome was 25 miles from the walls of the ancient city.
17:41Steve's come here to understand the challenges for himself.
17:46Getting water back from here means crossing hills and valleys and an open plain.
17:51Today, we overcome these problems with mechanical pumps and pressurized pipes.
17:57This is your element.
17:59Let's go.
18:01All the ancient engineers had to help them was gravity.
18:05The fact that the spring is 1,000 feet higher than the city.
18:10I think it's incredibly impressive how the Romans supplied water entirely by gravity from the mountains into the city of Rome.
18:20The engineers couldn't go over the mountains, so they had to go through them.
18:29And then, using a simple fluid level, they had to get the perfect gradient.
18:34Dig at too shallow an angle, and the water simply wouldn't reach Rome.
18:40Too steep, and it would erode the walls.
18:43The tunnel would collapse.
18:45What sort of gradient do these tunnels have to be laid out?
18:48The gradient was really very low.
18:51We talk about one per thousand, so it means one feet every thousand feet.
18:56That's why they normally had to make an aqueduct that was longer than the real distance.
19:02Keeping that gradient constant meant that the engineers needed, in effect, to create extra work for themselves.
19:09Building in twists and turns, finding a longer route.
19:13This aqueduct travels 50 miles, even though the straight route is just 25.
19:23The biggest surprise for me about the aqueducts is the accuracy of construction.
19:27And the way they did it is they had surveying checkpoints at about 1 to 200 feet across the entire length.
19:33Between those points, actually, the tunnels can meander, and the head height can change quite a lot.
19:38But what is consistent is the base flows at that consistent gradient from out here in the mountains, right into the city of Rome, 25 miles away.
19:46The Romans faced their arches with stone.
19:50Chris is using wood.
19:53But the Roman arches are 3,500 times longer, and transported almost 50 billion gallons of water a day.
20:03But they had years of aqueduct building experience.
20:07And this is Chris's first attempt.
20:10He leaves it to dry in the Louisiana sun.
20:14An aqueduct is so much more than just a bunch of arches through a valley.
20:21There's actually five different components past the water source.
20:24The first one of which is a tunnel.
20:26The second is a pipe system, which empties into a covered trench, which empties into the exposed portion of the aqueduct, which is the wall, and then the arcade.
20:36It's only when we see all the pieces together that we begin to understand the engineer's vision and skill.
20:43The terrain between the source and the city doesn't just conveniently slope gently downhill.
20:49It's marked by two valleys.
20:51The water was able to travel through deep valleys based on a change in elevation in the pipe system.
20:56So as you can see behind me, the far hill has a higher elevation, which would create a pressure to push the water through the pipe system and back up the hill nearest to me.
21:04On the downhill slope, water gains speed and pressure.
21:10This forces it up the slope on the other side, a solution that works on any scale.
21:17The water is now flowing with a constant rate, and that's based solely on gravity alone.
21:23Now, our aqueduct is, for the most part, level because it's impossible for anyone to build on the tolerances that the Romans use in their aqueducts.
21:29Chris's aqueduct build is a success, but its construction is only the start, because once it's up and running, it's never meant to stop.
21:39Now, our aqueduct is three months old, but it has already begun to crack because that's what concrete does.
21:46Now, these are similar problems that the Romans would have encountered with their systems, but this is a reminder to us that it's not just a structure, but this is a machine that supplies water to the city.
21:54So back in Rome, Steve's investigating how they maintained it.
21:59What I can see here is stone projecting from the pier.
22:03And this only happens on maybe once every eight or nine piers.
22:07And I can actually see that some stone has been hacked off in this position here.
22:12I think there are two purposes to this buttress.
22:14One is a stability system that provides lateral stability to the entire aqueduct.
22:20And the second is that it's a staircase where they can actually climb up and get into the lower aqueduct to clean it out.
22:27So it's both a means of maintenance and a means of stability.
22:30Very Roman in that they built it once and they used it twice.
22:33The stone buttresses once reached out about three feet, strengthening the structure.
22:41With a 40-foot climb carved into the buttress, the cleaning teams had permanent access, ensuring a constant water flow to the city.
22:50Around 300 gallons for every Roman, every day.
22:54Almost three times the amount the average American town supplies each of its citizens.
22:58But the Romans didn't merely rely on water, they loved it.
23:03To them it meant power, success and luxury.
23:08And that idea led to the creation of some incredible buildings.
23:12One of which presents a unique engineering challenge.
23:15How do you build a bath that will hold 10,000 people?
23:28Leading structural engineer Steve Burrows is in Rome to unearth its ancient engineering secrets.
23:35Rome's builders face the same kind of challenges he faces every day.
23:39And he wants to understand how they solve them.
23:43The baths of Caracalla.
23:46They form one of the largest, most complex structures in the city.
23:50They covered 25 acres.
23:5210,000 people could use them on any given day.
23:56It was really part of the culture of Rome.
24:00You have to think of this as almost like a really gigantic health club where people would come, they would meet, they would do business, there were gymnasiums, there were art galleries, even a brothel.
24:11But at the heart of it all was the ritual of bathing.
24:15That's what this building was made for.
24:17So as you move through the outer complex you come to the kind of the main bathing area.
24:23The first room you come to is the frigidarium.
24:26It's a cold room, it has cold plunge pools so you can go in and wash off.
24:31And then you progress through into the tepidarium which has got warmer water.
24:35You're slowly starting to heat your body up.
24:38And then the final space is the caldarium.
24:41Now this is really the heart, the centre of this vast complex.
24:45Seven hot tubs encircled the room.
24:50The vaulted ceiling was 111 feet high and it was all kept at a scorching 100 degrees Fahrenheit.
24:57Keeping a complex running with heat and water on this vast scale is a big task for any engineer, then or now.
25:05The 25-acre space beneath the baths is packed with tunnels, the veins and arteries of the complex.
25:12Never seen by the bathers in ancient Rome and rarely seen today, its heart was a battery of furnaces kept ablaze by the blood and sweat of hundreds of slaves.
25:24All right, here's a good example of one of the furnaces.
25:28The energy source was wood, maybe 10 tons a day.
25:33Up above I call this an engine room, but it's far more than that.
25:36It's actually an engineering complex right underneath the baths of Caracalla.
25:40This road that we're on here has furnaces on each side, so all of them are going to be belching smoke and delivering heat right from this fire pit here.
25:52A large wood-fueled fire raged on the platform, one of 50 in this subterranean boiler room.
26:01They heated vast volumes of water and air, and they never went out.
26:05This thing went through 10 tons of wood a day. That's 3,650 tons a year.
26:14And in order to supply that, it had to come through a network of distribution that covered the whole empire.
26:20From all of these distant places, materials were being shipped in to here, to Rome.
26:24And what I find particularly incredible is that that network and that continuous flow of materials ran for 400 years uninterrupted.
26:37So I suppose it's a bit like a car assembly plant.
26:40You know, the pieces come from a long way away, they're all brought together in one place,
26:44and they have to be brought just in time and just in sequence for the whole thing to work.
26:48It's a perfect example of strategic planning, Roman style.
26:55It took several million bricks to build this engine room.
26:59The huge temperature generated here had to be transferred 25 feet upstairs to heat the baths.
27:05But the hot air was thick with soot. How did they transfer the heat without the dirt?
27:11Steve investigates.
27:13So what we have here is a hyper cost.
27:14And the way this works is that this space above the floor is actually the heated zone.
27:20So the air passes under the floor and transmits its heat through this concrete slab, which is really thick.
27:26The reason it's thick is so that it has a high thermal mass.
27:29And what that means is it takes a while to heat up.
27:32But once it's heated, it retains that heat for a long time.
27:35A hyper cost is an underfloor heat exchange.
27:38The hot air from the furnaces fills the space under the floor.
27:41The concrete slab heats up and radiates its warmth into the space above.
27:47And they found a further use for this hot air.
27:50So once the air is passed under the floor, it then goes up behind the walls and eventually out through chimneys in the roof.
27:56As it does so, it passes through terracotta pipes embedded in these walls, which act as radiators.
28:01So they also heat the space inside this area.
28:05So what you get is an effect where all of that, all of that air from the furnaces is actually used to heat these spaces without people actually coming into contact with it.
28:14Seven million cubic feet of concrete, 10 million bricks, whole forests to fuel them.
28:19The emperor's baths operated on an industrial scale, delivering production line luxury to the masses.
28:27Caracalla is not building his baths out of the kindness of his heart.
28:30He is building it as a testament to imperial power and also as a means to keep the masses happy.
28:36As a Roman, think of the things that you had at your disposal.
28:41You had clean water, you had magnificent baths that you could go to, and you also had endless entertainment.
28:49So for a first, second or third century Roman, this was a pretty good deal.
28:55The baths are a hallmark of the Roman's fearless approach to problem solving.
28:59No challenge was too great.
29:02And, armed with revolutionary designs and materials, they began to build in ways which had never before been possible.
29:18Our team of experts is on a mission.
29:21To uncover the secrets of ancient Rome by thinking and building like a Roman.
29:25Now, they have a new feat of engineering to demystify.
29:30150 miles south of Rome, at Baia, is an initial attempt at one of the most difficult structures of all.
29:38More than 2,000 years ago, the Romans started building domes.
29:43Prior to the Romans, there are fundamentally two ways of creating interior space, of making a roof.
29:50Now, the first is post and beam.
29:51You basically have a forest of columns, and then between those columns you have beams.
29:58And what dictates the distance between those columns is the ability of this, the beam, to span.
30:04Now, if that's stone, they have to be quite close.
30:07If it's timber, they can be wider, but it's still the size of the single tree that you get that can dictate the distance between the columns.
30:14The second way is to create a truss, a simple truss roof.
30:19So, let's say you have two walls.
30:21Between that you have a triangular truss shape, much like the thing you see on top of a house, which would have simple cross struts inside of it.
30:28But again, the size of that is pretty much dictated by the size of the trees that you can get.
30:33But what the Romans did was created and perfected the concrete dome.
30:41In the first century BC, this structure, now half submerged, was a cutting edge experiment in construction.
30:49I'm wondering what they actually knew about concrete at this time.
30:52How long have the Romans been working with concrete?
30:54A couple of centuries by this point, it's really a try and tested method.
30:58What's audacious here is really the scale of the room that they're spanning.
31:03It's incredible to imagine the confidence of the people who built it.
31:08They will have had to have placed concrete on top of a wooden support structure.
31:14The only way this room could have been built was with a gigantic network of scaffolding and a canopy of wooden formwork.
31:24Then, inch by inch, 1.7 million tons of concrete is packed in by hand and left to cure.
31:33And then came the moment of truth.
31:36Whenever you build a structure like that and temporarily support it and then remove the temporary support and expect it to stand,
31:43it's a pretty exciting moment because if there's a failure, it will collapse.
31:48When the supports came down at Baia and the roof held, the Romans had made a massive leap forward.
31:54They'd created a huge space, roofed without pillars or columns.
31:59But the outside of the dome was far from perfect.
32:03Most of the structure is underground because the engineers relied on the hillside for support.
32:07This is fine for a prototype, but they were determined to do better.
32:13If they could make it freestanding, they could enclose any open space.
32:18And the possibilities would be endless.
32:21So what's so tough about building a dome?
32:25Dr. Chris Carroll and his team in Louisiana are about to find out.
32:29They are going to build their own version of the most complex, perfect building the Romans ever created.
32:36The Pantheon.
32:38Their starting point is the circular supporting wall.
32:41Now go ahead and measure the four-foot radius in the center of the circle.
32:46The Pantheon probably takes the most thought when it comes to how are you going to build it.
32:53Chris and the team are off to a good start.
32:56In Rome, Steve examines the real thing up close.
33:01The Pantheon.
33:025,000 tons of concrete defying gravity.
33:09Just look at the scale of that, damn.
33:12With a little squeeze, the Statue of Liberty would fit in here.
33:19It is in plan a circle of 142 foot in diameter.
33:25And in section, it is 142 feet high with a dome at the top half.
33:30And it is like that because you could then fit a perfect sphere within the building.
33:36And fundamentally, you are inside a perfect piece of built mathematics.
33:44It's just an incredible building.
33:46But what's great about it is it's all structural engineering.
33:50It tells its own story.
33:52So what's going on here?
33:54What we've got here is this massive weight that's bearing down at this arcade level here,
33:58at the top of this arcade level.
34:00And what that's doing is it's creating huge vertical forces that have to be transmitted down to the foundations by lots and lots of structure.
34:09But they've beautifully hidden it in the walls.
34:12The real work is done by eight strong points, or buttresses.
34:17They carry the dome's weight.
34:19And that means that the gap between them can be opened up.
34:23They're made into usable spaces all the way around the perimeter.
34:26So that you get this sense of this incredibly massive dome sitting on a light structure.
34:34A trained eye can see how it was done.
34:38You can see, looking at the outside, some of the internal structures poking through to the outside skin.
34:44What we've got here are these huge relieving arches, about 40 or 50 feet spans.
34:51This structure is far stronger than an ordinary brick wall.
34:56The arches are built into the brickwork.
34:59If they weren't there, traveling all the way around the drum in which the dome sits, the whole thing would come down.
35:04These relieving archers are doing their job.
35:08Their intention is to transfer the huge compression forces from the weight of this massive structure down those buttresses.
35:15And protect some of the weaker areas of structure below.
35:19So if the Pantheon looks simple, it's because its design is highly complex.
35:24Chris Carroll, although he's a doctor of engineering, has never built anything like this.
35:30This is by far the most complicated thing I've ever built.
35:34And with the Pantheon, there's a lot of different aspects you have to take into consideration.
35:40The way that we did it was just with the form work and created the shape of the arch.
35:45Looking good.
35:47And he's made a few other simplifications.
35:50No buttresses, just a thick, continuous wall.
35:54Break it up, Henry!
35:56Here, hit it that way, and you get more leverage.
35:59The Roman way of doing this was to build two brick skins.
36:04And as they rose, fill them with concrete.
36:07Walls on this scale aren't a problem.
36:10But the dome is a challenge.
36:12If you think about it with a dome, it's basically an arch.
36:14It is three-dimensional.
36:16And it all tries to compress at the top.
36:19No modern engineer would build a dome as big as the Pantheon without using metal reinforcements.
36:26But the Romans just had concrete.
36:29And that meant they had to be clever.
36:32Really clever.
36:33The wall has a concrete core, but the aggregate changes as you go up.
36:38So it gradually gets lighter.
36:40In fact, all the way through the dome, too.
36:42And it's basically layered like a cake.
36:45It was all in the concrete mix.
36:47Near the base, they used heavy stone.
36:50And by the time they got to the top, they were using pumice.
36:54A volcanic rock filled with air.
36:57And the dome gets thinner as it rises, from 19 feet at the base to just over 5 feet at the top.
37:05The Pantheon's dome is a piece of precision engineering that has stood for 19 centuries.
37:12The Louisiana model is brand new and a great deal smaller and simpler.
37:17But they're both built according to the same principles.
37:21So for Chris, it's time for the acid test.
37:24Is the design as strong as he thinks?
37:35Our team of engineering specialists is in the thick of recreating ancient Rome.
37:40Testing construction techniques first pioneered 2,000 years ago.
37:46So what can they discover about the Pantheon from their mini dome?
37:51This is our Pantheon.
37:52This is probably the hardest thing I've ever had to build, but it's probably also the coolest thing I've ever had to build.
37:57And we're curious to see how much the dome can hold, so we're going to do a simple test.
38:01What will it take to crush this unreinforced concrete dome?
38:06Dr. Chris Carroll starts with a wooden platform to ensure the load is evenly distributed.
38:10Then he piles weight on, 4,000 pounds, that's like a hatchback.
38:175,200 pounds, more like a station wagon.
38:22It's 7,600 so far, so we're about to go with another 1,200.
38:26More weight.
38:27The load sitting on top of the dome now is about as heavy as the dome itself.
38:33And still, it doesn't fail.
38:36But the sheer height of the blocks is becoming dangerous.
38:40We try to break it.
38:42We've stacked concrete over 8 feet tall above it and haven't been able to.
38:45Chris stops before this tower of concrete topples, but he's satisfied.
38:51It's pretty clear why the real Pantheon stands when other great buildings have gone.
38:56This makes me think that the Romans definitely knew what they were doing.
38:58I mean, a dome is a very, very strong structure.
39:02You can see that based on how high we've stacked the concrete.
39:05I mean, that's 16,000 pounds.
39:07A dome is one of the most difficult structures to build.
39:11But build it right, and it's a powerhouse.
39:13For almost 1,900 years, there's been nothing on earth to match the Pantheon.
39:20It took 20th century technology to significantly advance what the Romans invented.
39:27If you look forward to today's domes, we're able to introduce reinforced concrete,
39:33post-tension that reinforced concrete, use cable structures,
39:37and much lighter materials like fabrics to create huge dome structures.
39:40So dome technology today is a huge leap forward from Roman times.
39:45But what was created at the Pantheon was also a massive leap from the very first structure at Bayer.
39:51Only ancient Rome could have produced these buildings.
39:55With fabulous wealth, the spoils of war, its builders simply didn't need to worry about cost.
40:01When I think about the legacy of Rome, I think about imperial ambition, I think about a tremendous amount of resources.
40:12And I see how those came to bear on Roman architecture.
40:15But Steve Burroughs, an engineer who has himself built some grand monuments, knows there's something else at play here.
40:24Yes, they had limitless resources, but they also took on enormous challenges.
40:28The two things that strike me about engineering in Rome is that it wasn't so much a revolution as an evolution.
40:35They just got better and better over time.
40:38What I've seen is that skills were passed on from father to son, from generation to generation,
40:43such that when you look at a building like the Pantheon, what you see is pure perfection.
40:46They just got better and better at what they did.
40:48The second was this unique combination of ambition and opportunity.
40:53The Romans didn't appear to be constrained by finances, and they certainly weren't constrained by fear.
40:58When the Romans wanted to build something, they just did it.
41:02Chris and his team have built an aqueduct, a crane, and a dome, and come face to face with some of the challenges that tested the men who built Rome.
41:13This has been an incredible experience, and it's definitely given me a whole new respect for what the Roman engineers did.
41:19The builders of this city had the opportunity, the skill, and the courage to reshape their world, revolutionizing the way they lived.
41:31And although the empire would eventually fall, these awe-inspiring structures still stand.
41:37A lasting legacy to the pioneering science of Roman engineering.