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  • 5/25/2025
The marvels of Roman public architecture and hydraulic engineering are explored in a show that looks at the structure of amphitheaters such as the Colosseum. A little known feature of these amphitheaters is that they were originally roofed by canvas covers that were retracted when the arena was not in use. But how did the Romans devise a mechanism as tricky as a huge retractable roof? Our team of archaeologists and engineers will tackle the problem that the ancient Romans solved in one of the most striking examples of that civilization's ingenuity.

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00:00Nearly 2,000 years ago, the Emperor of Rome presented his subjects with a new gift.
00:16It was a monument of unprecedented scale, a marvel of architecture and engineering achievement,
00:26a testament to the power and glory of Rome, the Colosseum.
00:38Today, it's one of the most famous buildings in the world.
00:48Thousands of tourists flock to this site each day, but few understand the true nature of this ancient wonder.
00:58Because the Colosseum was not a sports stadium, this was a theater of death.
01:11In 1961, Dino de Laurentiis presented his vision of the Roman arena in the film epic Barabbas.
01:20Elaborate sets, complete with artificial hills and lakes and exotic animals from the far reaches of the empire, were all part of the ancient spectacle.
01:31But in the early 1960s, Hollywood could not show the one thing that the ancient audience came to see.
01:40Blood.
01:44The blood of unarmed prisoners torn apart by wild lions.
01:53The blood of exotic beasts slaughtered for pleasure.
02:02And the blood of gladiators trained to fight to the death.
02:10For over 400 years, the Colosseum set the stage for mass murder.
02:22One typical day in the amphitheater could feature the executions of thousands of men and animals.
02:31The Colosseum was carefully designed to host these spectacular bloodbaths.
02:40Stretching over 600 feet end to end and covering six acres in downtown Rome, the Colosseum could seat over 45,000 spectators.
02:57The huge crowds were systematically herded to and from their assigned seats through 80 numbered entrances and stairways.
03:08Inside, the gruesome show was performed on a giant wooden stage, covered with fine sand to absorb the ever-flowing blood.
03:21The floor timbers have now rotted away, exposing a labyrinth of underground tunnels, cages, and cells for the doomed prisoners.
03:33As the show went on overhead, armies of stagehands negotiated the narrow hallways with fantastic props, machinery, and weapons.
03:47There were elevators and trapdoors so that beasts and gladiators could make dramatic entrances up onto the arena stage.
03:58But the most amazing construction of the Colosseum had nothing to do with the show.
04:04It was designed purely for the benefit of the audience, to keep them calm and content as the violent spectacle unfolded below.
04:14It was a roof.
04:18Even in the sweltering summer months, spectators at the Colosseum could remain cool and comfortable,
04:25thanks to an enormous roof that extended over the seats and protected them from the scorching Mediterranean sun.
04:34But not a shred of the original roof has survived.
04:39And the Colosseum's most spectacular feature is now its biggest mystery.
04:47What kind of roof could have covered such a huge building?
04:54Even today's engineers usually don't attempt to cover the entire stadium, but leave the playing field and some of the seats open to the sky.
05:10The few large arenas that are completely enclosed, like the Houston Astrodome, are spanned only with the help of steel supports and lightweight plastic fibers.
05:24But without modern materials, how did the Roman builders complete their awesome task?
05:34The largest surviving ancient roof covers the Pantheon, a temple to all the gods.
05:43Here, the Romans produced an engineering masterpiece, a magnificent dome that soars 150 feet above the floor.
05:55Although it looks lighter than air, the concrete dome exerts 5,000 tons of pressure onto massive walls, 20 feet thick.
06:08The roof of the Pantheon was an amazing achievement.
06:12But could the Romans have used the same technique to cover the Colosseum, a building that's four times as big?
06:20We asked structural engineer Chris Wise.
06:24If I was an engineer 2,000 years ago, I think I'd be in trouble at this moment, because if the emperor asked me to put a roof across here,
06:32I'd be trying to make a sort of technological jump from anything that we know the Romans ever did.
06:39And I could start with a flat roof, very simple, doesn't span very far, and would need in a building like this a forest of columns,
06:48which would just get completely in the way of the spectators. They wouldn't be able to see anything.
06:54Another solution would be to just try and increase the span a bit by using the new material, concrete, and to make a longer beam.
07:05And that's possible, but again, it would still need a forest of columns a bit further apart,
07:10and eventually it would get to the point where the concrete, which is very brittle, would just break, and it would just snap.
07:17So what it needs is a technological jump. And the Romans had that. They knew about arches, they knew about domes.
07:24And the nice thing about an arch is that you use the material for what it really is best at,
07:30and that's just pushing one stone or one piece of concrete against the next piece.
07:35You can make an arch that might span about 45 meters, which is about how far they managed at the Pantheon.
07:44And in an arch, each of those stones is pushing against the next one,
07:48and just taking the load very slowly and carefully from stone to stone down to the ground.
07:54I think it would be crazy to do a solution like that at the Colosseum.
07:57Although you could imagine it, it would end up looking like this.
08:00A concrete dome over the Colosseum would require supporting walls 25 meters or 80 feet thick.
08:15And the whole roof would be high enough to enclose St. Paul's Cathedral, or a modern skyscraper 30 stories tall.
08:25I think they had no option. They had to go for a very light roof over the amphitheaters.
08:29Because any permanent roof would have been crazy.
08:33There's evidence to support Chris' idea that the Colosseum had a lightweight roof.
08:40This is an ancient painting from the lost city of Pompeii.
08:45At the very top of the picture, suspended above the city's arena,
08:49is what appears to be a large, billowing cloth canopy.
08:55Was this the roof that covered the Colosseum?
09:00A few ancient Roman coins bear the image of the great amphitheater.
09:06None of them show the roof, but they do reveal a series of lines protruding from the top of the monument.
09:15Historians believe that these represent large wooden masts,
09:20which clung to the amphitheater's walls and supported a giant canopy, or awning, over the spectators.
09:30Architectural historian Rainer Graefa has been obsessed with the mysterious roof since he first heard of it 25 years ago.
09:39I got involved in the Roman tent roofs at the University in Stuttgart.
09:43And I got so enthusiastic that I forgot another doctor's thesis I just had begun and worked at, two years or more even,
09:53and began this research.
09:57To solve the mystery, Rainer examined amphitheaters throughout the Roman Empire,
10:02including this well-preserved stadium in Nimes, in southern France.
10:08Joining Rainer is Chris Wise.
10:12A leading expert on modern lightweight roofs, Chris is intrigued by the possibility of an ancient Roman version.
10:19The thing that I find is that it's so difficult.
10:22When you see an amphitheater, you just think that that's the finished thing.
10:26But really, an amphitheater without an awning is like a man without any hair.
10:32Yeah, very nice, really.
10:3770 feet above the pavement, Rainer leads Chris along the narrow upper rim of the stadium to an important clue.
10:46So what have you got here, Rainer?
10:48We spoke already about the mast holding the tent roof.
10:51And you can see very clearly the whole technique to hold the mast.
10:57They put in the top of the mast corbels, heavy stones sticking out, and they pierced it.
11:04They made a hole in it.
11:06And down in the corners, you see a second hole for the foot of the mast.
11:10Right, about two meters down.
11:12Two meters down.
11:13Three meters down.
11:14Two meters, exactly.
11:15Right.
11:16It would have been very beautiful when they had all the masts up.
11:19Yeah.
11:20It's fantastic.
11:21You must imagine.
11:22How many masts for the whole?
11:23120 masts around.
11:28The mast holes at Nîmes helped Rainer explain similar evidence found at the Colosseum itself.
11:36Here, 150 feet above the ground, ornamental stones jut out from the stadium wall.
11:44Rainer is convinced that these were the brackets that supported the giant masts seen on the ancient coins.
11:53Up until now, historians theorized that the masts supported a giant spider web of ropes,
12:01which in turn held a cloth covering over most of the Colosseum.
12:06But Rainer has come up with an entirely new theory.
12:13He believes that instead of ropes, the masts held horizontal wooden beams
12:18that projected over the seats and supported the broad sheets of the canopy.
12:24Rainer has had some trouble selling his theory to other experts, including Chris.
12:29If you like, the strength of the top of the Colosseum, for example,
12:33to see whether or not it could take the forces that this system would put onto it.
12:38To see who's right, Nova challenged Rainer and Chris to put their ideas to the test
12:44and reconstruct the lost roof of the Colosseum.
12:49Since the ancient stadium is off limits for new construction,
12:52Chris and Rainer travel to the town of Barcarata,
12:55in an area of southern Spain controlled by the Romans 2,000 years ago.
13:02They set up shop in a 15th century bullring.
13:07Here, a team of experts will try to solve the mystery
13:11by building two different versions of the ancient canopy.
13:15We've got one or two things planned for this old building.
13:17It's a 15th century castle in Spain.
13:20What we're planning to do is to put down on the sides a couple of rows of corbels.
13:27These are modern version of the old mast holders?
13:30It is modern, yes.
13:31In steel.
13:33Why did you change this detail?
13:36Because in the original Roman amphitheatres,
13:39obviously they would have put the stone corbels in as they were building the walls up.
13:43And we couldn't do that here without making an enormous hole into the wall.
13:48And so in the end what we've done is make a modern equivalent
13:52which has the same load carrying capacity, but made out of steel.
13:58The scale of this project is about half the size of the Colosseum.
14:06But it's still going to be a fairly tricky job
14:10because the big poles that we're moving around weigh about half a tonne each.
14:20The team's first job is to build a makeshift crane
14:23that can lift the large mass to the top of the bullring wall.
14:29Joining the construction crew is Brian Austin.
14:33Once a high wire walker, Brian is the largest supplier of circus big tops in Europe.
14:41His expertise in rigging poles, ropes and cloth has made him a millionaire.
14:46Do you use these in a circus crane?
14:49We use the sheer legs just to erect our main mast,
14:53which are anything up to 80 feet.
14:56Twice as long as this pole?
14:57Yeah.
15:04Down?
15:05Right.
15:06Once the crane is in place, the team will attempt to lift the first mast
15:1135 feet from the ground below.
15:15Pretty good.
15:18This big pole is going to cantilever over the end of the wall there,
15:22hang down a rope, and we're going to pick up the first mast
15:25and lift it from the bottom up into position.
15:28And then we're just going to tip it up very, very gently, very easily,
15:31absolutely no problem, and lower it into the corbels.
15:34Piece of cake.
15:40Brian's work at the circus has taught him the power of the pulling.
15:47The ancient Romans also recognized the mechanical advantage provided by this simple device,
15:53and they often exploited it in the lifting of heavy weights.
16:02Come in, come in.
16:05Come towards the front. Walk forward.
16:10Thanks to the pulleys, the first stage of the operation goes smoothly.
16:15But getting the 500-pound mast to the top of the wall is only half the job.
16:23The team now has to rotate the mast into a vertical position
16:27and slide it down into the corbel.
16:32Although Brian designed the crane himself,
16:35he has a sneaking suspicion that it's not quite tall enough
16:38to lift the mast to its proper height.
16:41What's worrying you?
16:42Because I don't think there's enough height there to get it high enough.
16:45It doesn't matter.
16:46Oh, it doesn't...
16:47If we move that, all we're going to do is...
16:52Well, you think at the moment that that's rope that we tied around the top.
16:55I don't think we can lift it high enough for us to tilt that there,
16:58to lower that into that corbel.
16:59Well, shall we try it and see what happens?
17:01Yeah, we'll get as much purchase on this end as we can.
17:03Yeah, that's it.
17:04And then we'll all come over and pull this way.
17:06Yeah, I think, and we'll stabilise it...
17:08Brian was right to worry.
17:10As they rotate the mast, it gets stuck at an awkward angle
17:14between the top of the crane and the bullring wall.
17:18Yeah, we need to go up now.
17:19Can you pull it? Can you raise...
17:20Yeah.
17:21Can you raise it?
17:22Yeah.
17:23Can you raise it now? Use the crane to lift it.
17:26Just a tad.
17:27Yeah.
17:28Right, it needs to go up now.
17:29The team struggles to loosen the mast,
17:31but this puts too much pressure on the crane.
17:34Just a tad.
17:35Yeah.
17:36Whoa, whoa, whoa, whoa, whoa!
17:37It's breaking, it's breaking.
17:39No, no, no. Up, we've got to go up a tad.
17:41We need another foot.
17:42Go on, keep going. Very, very gently.
17:44Brian, keep out of the way...
17:45With the crane threatening to collapse,
17:48Chris hopes to reduce the strain
17:50by gently easing the whole contraption to one side.
17:55I wouldn't do that.
17:56OK, this way.
17:59Just go slowly, go on.
18:01Pull it.
18:02Don't pull it, don't pull it down.
18:04The plan pays off, and with one last pull,
18:08the mast finally hits its target.
18:11You're there.
18:12OK.
18:13Is it in?
18:14It's in.
18:15Whoo!
18:16I'm still shaking, actually, because for a moment there
18:18I thought the crane was going to snap
18:20and everybody just get...
18:21go over the edge with the timber,
18:23but when you freed it all up near the end,
18:25it then went in as sweet as a button.
18:27Left, left.
18:29With the mast in place,
18:30the next step is to hang the horizontal beam
18:33that will carry the awning out over the seats.
18:37OK, now walk it round.
18:39Reiner got the idea for these wooden beams
18:42from the ancient painting from Pompeii,
18:44where the canopy seems to hang from rigid supports.
18:49The picture was important,
18:51but it was hardly a blueprint for a stadium roof.
18:56If long wooden beams were used,
18:58how did the Romans suspend them
19:00over the heads of the spectators?
19:04A possible answer came from an accidental discovery
19:07just outside the Colosseum.
19:11Historian Norma Goldman.
19:13Now, just below us here on the road,
19:16when a utility line, a gas main,
19:19had to be repaired,
19:21the repairman dug into a camp
19:24that has been identified as the camp
19:27for sailors from Mycenaeum.
19:30Now, Mycenaeum is almost 200 miles below us
19:34down on the Bay of Naples.
19:36What would a camp for sailors
19:40be doing here in the middle of downtown Rome
19:43next to the Colosseum?
19:45Obviously, the sailors were needed
19:48to handle the rope and the cloth.
19:51And even more compelling as evidence
19:53is the fact that the Latin word for the awning,
19:57the sails, is the word vela,
20:00the same word for sails on ships.
20:07This replica of an ancient ship
20:09shows the basic design used by the Romans.
20:14The sail hung down from a horizontal boom
20:18that was suspended from the top of the mast.
20:21Reiner believes that when it came time
20:23for the Romans to build a cloth roof for the Colosseum,
20:27they simply multiplied the number of masts
20:30and hung the sails between the booms,
20:33side to side instead of up and down.
20:39Back at the bullring,
20:41Reiner needs some nautical expertise
20:43to rig his canopy.
20:48Owen Roberts is a lifelong sailor,
20:51boat builder, and an expert on ancient ships.
20:56Using the Roman ship as a model,
20:58Owen simply hangs the boom off-center
21:01so that once it's swung into position,
21:03it will project further out over the seats.
21:08Chris doesn't believe that the Romans used wooden booms,
21:12and when he's done helping Reiner,
21:14he plans to build a model of the roof
21:17that does without them.
21:19Well, let's turn it around and then fix it.
21:21As a modern engineer,
21:22he works mostly with synthetic materials,
21:25and today he's uneasy about putting too much pressure
21:28on the giant pieces of timber.
21:30We have to be very careful with the mast,
21:32because we're forcing it in the bottom,
21:35and also these top sections, as we're turning it around,
21:38the ropes have got to pivot around there,
21:40so we have to just be careful.
21:42The worst thing that could happen is the mast could either,
21:45because there's a lot of force going down here now,
21:47as you can imagine,
21:48the mast could go through the corbel at the bottom,
21:51or if it got really tightened up as we're swinging it around,
21:55we may have put too much bending in the mast,
21:57and it could snap just at the level of the top corbel,
21:59just down under here.
22:06There we go.
22:12The mast is rotating a little.
22:14Unlike Chris, Owen has decades of experience
22:17with wooden masts and booms,
22:19and he's confident that the poles will bend, not break.
22:23Yeah, that's good.
22:30Brilliant.
22:33Okay. Whoa, whoa, whoa.
22:35Fantastic.
22:37Brilliant.
22:39Yes!
22:41It works.
22:46Over the next day,
22:48four more masts and booms rise above the bullring.
22:55All with the rigging of ancient Roman ships.
23:03The next step is to hang the canopy,
23:06and sailor Owen has brought along
23:08several hundred square yards of canvas to do the job.
23:11Right, here we are.
23:13Let's open it up a little bit more.
23:18Norma Goldman joins the crew
23:20as they begin the task of attaching the canvas to the beams.
23:24These rings on the top...
23:26Let's just see if we can get it up.
23:28Whoa, there we go.
23:30The team is building a small-scale version of Reiner's awning
23:34that will cover just a segment of the bullring.
23:37Rigging the canvas should be simple,
23:40but they suddenly run into a major snag.
23:43That little hook there,
23:45that loop has got to go over the end of the beam.
23:48That goes on first, so that's slid along like that.
23:51In the construction rush,
23:53someone forgot to attach a crucial rope to the end of the booms
23:57before swinging them over the seats,
23:59and without it, they can't rig the canopy.
24:02How are we going to get out there?
24:04How would they have done it on a sailing ship?
24:07On a sailing ship, yes.
24:09They would not sit on it, it's too dangerous.
24:12They have ropes under it to stand on.
24:14A rope underneath?
24:16What's this about foot ropes?
24:18Foot ropes, yes, these ropes you're talking about.
24:21They weren't invented until about 1600 A.D., this is.
24:24This is 1,600 years.
24:26So I think you either need to get somebody out on top of this,
24:30walking along and then edging along,
24:33which is quite possible.
24:35They can still hang on with one hand, can't they?
24:38Sure, they've got that rope there.
24:40Would you do it yourself?
24:42If I was about 20 years younger, yes.
24:44All right, let's try it then.
24:46Although the Romans would not have made the same mistake
24:49as our novice crew, the ancient riggers probably did need
24:52to get out to the ends of the booms for repairs.
24:55Construction supervisor Michael Rourke
24:57offers to play the part of an ancient mariner
25:00as he attempts to deliver two ropes to the end of the pole,
25:0430 feet above the seats.
25:07The rope's going to twist at the end.
25:10Mike volunteered with enthusiasm,
25:12but as he inches out into midair, he's having second thoughts.
25:17This is not a good idea.
25:19I'm coming back, I can assure you.
25:22We haven't cracked it then,
25:24because it was about 30 metres up in the air at the Coliseum.
25:27I mean, this is a big enough drop from here.
25:34I think we didn't plan it in the right way.
25:37I also think Mike isn't used to going out on a spar like this.
25:40I think if we'd had a seaman who was used to it,
25:43he'd probably walked most of the way and just fitted it over the end.
25:46He might have sat down at the last minute,
25:48but he'd been quite happy on that.
25:50Yes, indeed, but you're not used to doing this.
25:52But I think a sailor, as I say, from that period,
25:55would wander out quite quickly, do it, and be back in no time.
25:58But here, unfortunately, we'll have to use a ladder, won't we?
26:01They wouldn't have had a 30-metre ladder in Rome.
26:04Just as the crew is ready to give up and use a ladder,
26:08Reiner remembers an important feature about the booms.
26:12But what is for me new now,
26:15the importance of being able to swing the beams out and in.
26:19Yes.
26:20This I didn't think about before.
26:22We know we can also lower them.
26:24Lower, yes.
26:25Just keep the load on it.
26:28Oh, yes.
26:29Keep the load on it. Got it?
26:31All right, here we go.
26:33Because the booms are suspended from ropes,
26:36they can be manoeuvred backwards, forwards, up or down.
26:40Can we have another man to help Reiner?
26:45Here at the bullring, the quickest solution is to lower the boom.
26:49Down, down, down, keep going, keep going.
26:52Whoa, that's it, that's it.
26:54The ends within reach,
26:56the real job of rigging the canopy can finally begin.
27:05Rings on the bottom.
27:07Rings on the bottom or the top?
27:09All right, so take the corner over there, take a corner over here.
27:12That's fine.
27:13Owen has designed a complicated system of ropes and rings
27:17that only a sailor can comprehend.
27:25It's not too bad at this stage.
27:30Just tie a bow in on that.
27:33Then we've got everything pulling against each other, haven't we?
27:37What I did was to shove it through there.
27:44You can see now why the rings are on top,
27:47so that the canopy will lie evenly and not drag across the...
28:03OK, stop.
28:05With the booms loaded with the canopy,
28:07Chris relies on interpreter Ignacio Arteaga
28:12to coordinate the final raising of the roof.
28:21And again.
28:23Once more.
28:27And once more on this side.
28:32And once more.
28:37And now tie them off.
28:41And now tie them off.
29:11And now tie them off.
29:32This is the roof I imagined always to have been over the Roman buildings.
29:37And you see some details are a bit rough,
29:40but as a whole, it's a very beautiful roof.
29:43It gives us a good impression of the old construction.
29:49It looks very similar to the roof shown of the famous wall painting of Pompeii.
29:55We have here the beams,
29:57and we have the awning hanging on the beams, the strings.
30:02It went around. It was a circle.
30:06Reiner's reconstruction gives us just a hint
30:09of how the magnificent canopy might have looked
30:12as it fluttered over the Colosseum.
30:18At the ancient stadium, wind and rain long ago
30:22dissolved every trace of wood, rope and cloth
30:25that made up the giant roof.
30:28In fact, much of the building has been destroyed
30:31by two millennia of decay and abuse.
30:35Earthquakes toppled half of the stadium's limestone façade,
30:40and scavengers stripped away the marble benches and statues.
30:48The remaining shell of the monument only survives
30:51because of a unique and durable building material
30:54developed by Roman engineers,
30:57concrete.
31:00Concrete not only made up all the internal passageways
31:03and supports for the seats,
31:06but it also formed a massive foundation
31:09for the entire structure, 40 feet deep.
31:15What made Roman concrete so special?
31:18The answer lies 150 miles south of Rome
31:21at the foot of the infamous volcano Mount Vesuvius.
31:31Here, historian Norma Goldman
31:34found the Roman engineers' secret ingredient
31:37on the beach.
31:40The sand produced from the several volcanoes
31:43from this section of the Bay of Naples
31:46had an amazing quality.
31:49When workmen mixed it with lime,
31:53the powder became cement.
31:58And when they mixed cement
32:01with gravel or rubble,
32:05that's called aggregate,
32:08and water,
32:13they got concrete.
32:16The Greeks first invented concrete,
32:19but their mixture could take years to harden.
32:22The Romans perfected the recipe
32:25by adding volcanic sand.
32:28The porous nature of the sand created a concrete
32:31that would set in record time.
32:41And Roman concrete had another useful quality.
32:45It sets underwater.
32:49And the longer it sets,
32:52the harder it gets.
33:03The Romans used this cheap and durable material everywhere.
33:09From the British Isles to the deserts of the Middle East,
33:12concrete fueled an explosion
33:15of monumental Roman construction.
33:38Back in sunny Spain,
33:41Reiner's canopy is a big hit
33:44with the local construction crew.
33:47But praise for the 20-foot wood-supported awning
33:50has not been unanimous.
34:00Reiner, Chris and Owen do agree
34:03that the wooden booms that support the canvas
34:06could extend to about 100 feet before breaking.
34:09But would this be far enough at the Colosseum?
34:14Although entrance to the Colosseum was free,
34:17the seating was strictly segregated.
34:20The worst seats were under the portico,
34:23where wooden bleachers were set up for the poor
34:26and for women.
34:28In the rest of the stadium,
34:30the marble seating was assigned to men
34:33according to wealth and social status.
34:36The windows immediately surrounding the arena
34:39were reserved for senators, knights
34:42and Rome's holiest of women, the Vestal Virgins.
34:46The emperor and his family had the best seats of all,
34:50in a private box directly above the stage.
34:53Chris believes that an awning
34:55that extended only 100 feet from the masts
34:58would never reach the seats
35:00of the wealthiest and most important spectators.
35:03I can't see why a system like this,
35:06which only covers half of the seats in the Colosseum,
35:09is the method for the Colosseum.
35:11Why?
35:13You must imagine it's 2,000 years ago that they did it,
35:17and when we read that they covered
35:20the auditorium of the Colosseum,
35:22we know it's a very huge space.
35:25We have the wish to cover it totally,
35:28but they couldn't do it.
35:30They couldn't do it using this method.
35:32There's another way of doing it,
35:34using the same materials, the same rope,
35:36the same timber for the mast, the same canvas.
35:39I think that if we simply put up some masts
35:42and slung a rope from side to side,
35:45a little bit like a suspension bridge,
35:47like a modern suspension bridge,
35:49we would be able to carry the canvas
35:52significantly further than we would do with this.
35:56Keep going! Keep going!
36:00Come on! Keep going!
36:02Unsatisfied with Reiner's beam method,
36:05Chris now wants to build his own version of the ancient roof,
36:09relying heavily on a single material, rope.
36:20Before Reiner came up with his wooden boom theory,
36:23most historians believed that the ancient canopy
36:26was held up by a spider web of ropes.
36:30Just starting to lay out the very first segment
36:33of the rope system.
36:35Although the theory has been around for a couple of centuries,
36:39no one has ever tried to reconstruct
36:41a working model of the rope canopy,
36:44and it's now up to Chris to figure out
36:46all the practical details.
36:48At this point here, it's going to be the top of the mast.
36:52It's the one we put up.
36:54His first discovery?
36:56If rope were the main support for the roof,
37:00the Romans needed a lot of it.
37:02And then back here, this point is going to be tied
37:05to the end of the pole that we put up this morning.
37:08Even for an arena half the size of the Colosseum,
37:11Chris's design will require a monumental four miles of the stuff.
37:17To support the ropes, Chris has erected several 40-foot masts,
37:23and local riggers are assigned the delicate task
37:26of delivering the necessary lines straight to the top.
37:32This is where the canvas goes under here, okay?
37:35Like that.
37:37Double, double...
37:38In theory, Chris's roof will work like a suspension bridge.
37:43One set of ropes is strung between the tops of the masts
37:47surrounding the arena.
37:49Spaced along these upper ropes,
37:51a series of vertical drop lines runs down
37:54and supports a lower set of ropes that carries the canvas awning.
37:59But achieving the elegant simplicity of his plan
38:03may be more difficult than Chris imagines.
38:06Run the ropes loose.
38:08Hang on, that ain't going to work.
38:11Hang on, that ain't going to work.
38:13We've got 10 metres there, and we've got 8 metres here.
38:17We're already 2 metres short of how to tighten it.
38:20Big top expert Brian Austin has some doubts about Chris's design.
38:24We would need to have a set of pulleys on the ground here
38:27which you can then pull up.
38:29To complicate matters, there's been a delay
38:31in the delivery of supplies to the bullring,
38:33and there aren't enough pulleys to properly tighten
38:36the four miles of rope in the roof.
38:38Bring the load down here, back through there.
38:40We haven't got the pulleys.
38:42We've got to do it with the equipment that we've got.
38:46So what we've had to do is invent a few ways
38:51of getting ropes through things with a minimum amount of friction.
39:00Chris's determination is typical of his ancient predecessors.
39:05Roman engineers were constantly overcoming major obstacles
39:09with their innovative building techniques.
39:12Give us that rope, and we'll tie it off here.
39:14Their success was instrumental in extending Rome's power
39:18across 2 million square miles of territory and into Spain.
39:29Just a few miles from the bullring lies the ancient city of Merida,
39:33once the capital of Rome's westernmost province.
39:40Like dozens of other Roman cities,
39:43Merida features a showcase of civil engineering projects,
39:47complete with bridges, bathhouses, and extensive public waterworks.
39:56Although Merida was built on a strategic site on a river,
40:01no self-respecting Roman hydraulic engineer
40:05would allow people to drink from that polluted river water
40:09into which all of the sewers of the city flowed.
40:12Nothing was too difficult for them, though,
40:15in finding a source of freshwater.
40:17They came out to higher ground north of the city
40:21and built two huge dams,
40:24this one covered with granite 45 feet deep.
40:31And from the dammed reservoir,
40:34water was then channeled through underground conduits.
40:4012 miles toward the city, following the contours of the land.
40:47And where there were hills, they went through them.
40:51Where there were shallow valleys, they covered them with low aqueducts.
40:57And where there were deep valleys,
41:00they covered them with the high-arched aqueducts
41:04so that the water could be brought to the city
41:07for bathing, for drinking, for the fountains.
41:15This is one of the few genuine Roman baths still in existence.
41:20I'm in the women's section,
41:22but there's an identical section right next door for the men.
41:26Women came down not only for bathing and for healing.
41:31They came down for social reasons, to gossip,
41:34to talk about the new blonde German wigs that were coming into fashion,
41:39to talk about the vulgar play last night in the theater,
41:44and perhaps to arrange for the engagement of a 12-year-old daughter
41:49who was now ready for marriage.
41:53Another very extravagant use of that precious water from the reservoir
41:59could have been in this Merida Amphitheater,
42:02for it is most unusual in having waterproof cement
42:06lining the surfaces of this depressed area.
42:10And what for?
42:12For water to have flooded the entire area
42:16and small craft or miniature boats brought in
42:20to reenact mock naval battles,
42:23and the condemned criminals or slaves who were put aboard
42:27fought to the death.
42:36Back at the bullring, Chris is plowing ahead with his rope canopy.
42:43For his roof, Chris is using 2 1⁄2 times as much canvas as Reiner's design.
42:51At the Coliseum, the same design would require
42:55over 200,000 square feet of cloth,
42:59enough to cover four football fields.
43:02Just realize we've got to have the top rope above the bottom rope
43:06when we tie the canvas on.
43:08Otherwise we won't be able to lift it through.
43:10So if this isn't above here,
43:12we can't lift it up when we finally do the roof.
43:17Chris's enthusiasm for the project
43:19is not shared by the other members of the team.
43:22Sorry.
43:24Say sorry, guys.
43:26Sorry, guys.
43:28Thanks.
43:30Brian is still troubled by doubts.
43:33And the masts are only 9 1⁄2,
43:36plus the top rope then goes 9 1⁄2 meters above the bottom rope.
43:42Plus the top rope then goes 9 1⁄2 meters above them.
43:47And there is no mast.
43:49So we're 9 1⁄2 meters short on the mast.
43:52OK, for this one...
43:54Can you put that in simple English?
43:59It isn't going to work.
44:01What isn't going to work?
44:03We aren't going to get it up.
44:05Why?
44:07What we need to do at some point is to tighten the lower rope.
44:11Yeah.
44:13And all the sails are connected around the back.
44:15Right.
44:17So they would have to either be untied
44:19or they'll just get torn as we tighten it up.
44:22Chris plans to raise the roof by tightening only the upper ropes.
44:27But Brian fears that if the lower ropes are left slack,
44:31the slightest bit of wind might set the roof flapping uncontrollably,
44:35and that could destroy the canvas.
44:39Yeah, I mean, it's not going to be perfect,
44:41but it would be perfect if we had the pulleys to adjust everything.
44:44Yeah, but if we had the pulleys to adjust the back now,
44:46the sails are around the inside of the poles.
44:48So if you tighten the rope backwards, we're going to tear the sails.
44:51And we're not touching that?
44:53No, because we're not going to actually do it properly.
44:55We're going to end up offsetting it.
44:57It'll work absolutely fine, it'll look absolutely beautiful, believe me,
45:00by tensioning the bottom ropes over there.
45:03OK.
45:06Ignacio, start with this first one.
45:14As the crew scurries to attach the canvas to the ropes,
45:17Reiner retreats to the top of the bell tower overlooking the bullring.
45:22With his bird's eye view, Reiner can see bad news for Chris on the horizon.
45:29I would have been fine if we'd been doing this three days ago
45:31because it was completely flat calm.
45:33But over there is an enormous black cloud which is coming over with wind.
45:39And behind me is a big sail, which eventually I hope will be a roof.
45:44And I think it'll be OK.
45:47The most important thing is just to explain to the guys
45:50so that they know precisely what they're supposed to be doing
45:52and they don't pull out of sequence.
45:54We know that the wind will catch underneath the canvas and lift it right up.
46:02When that happens, just hang on, don't panic.
46:11After two tedious days of looping, threading and knotting,
46:15the four miles of rope and thousands of square feet of canvas are finally in place.
46:20And it's time to put Chris's theory to the test.
46:23Can you take up the slack on that one?
46:27In order to raise the giant canopy safely,
46:30the four teams of men positioned at strategic points around the bullring
46:34must pull their ropes precisely on cue.
46:37Can you go up there, please?
46:39Yeah.
46:40OK, we should lift.
46:41Right.
46:50Owen, can you pull yours?
46:54Keep going.
46:55Keep going.
46:57Keep going.
46:58Keep going.
47:00Mike, can you keep going your side?
47:02Yeah, hold.
47:16OK, well, tie it off.
47:21Chris hopes the approaching wind will actually help lift the roof to its proper height.
47:27Tighten up the top rope.
47:30But as the first gusts attack the awning, Brian senses trouble.
47:37Yeah, you want to be getting it together now because you're going to lose the lock.
47:41You will do if you want to get it even now.
47:44No, they can tie it off.
47:46Just as he predicted, the lines holding the canopy are too slack and thrash violently.
47:52There's no tension on the bottom, and that's the opposing side to the lifting.
47:58The canvas can't take the pressure and starts to rip right off the ropes.
48:03Self-destruction.
48:14In an attempt to stop the billowing,
48:16Brian does his best to tighten the lower ropes that carry the canopy.
48:21Without any pulleys, it's nearly impossible to get the ropes completely taut.
48:26Brian's strength and skill are all that's holding the roof together.
48:37Eventually, Brian's last-minute efforts pay off,
48:40and he's able to tighten the ropes just enough to stabilize the canopy.
48:46The interesting thing is Brian's now stressed up the bottom ropes,
48:50and you can see it's started to stabilize.
48:52The rope structure itself is holding together very well.
48:56As the windstorm subsides, the roof finally takes its intended shape.
49:06The system itself is obviously one that does work,
49:09but the coordination in the erection kind of went to pieces.
49:13As soon as we got it up, we had no control over it,
49:16and as you can see, as I managed to coddle something together just to shorten the bottom,
49:21we get the true effect of what we set out to get.
49:28Yeah, I am pleased.
49:29I mean, we've proved that it can be done.
49:31It's not perfect, but I think within the limitations of the time.
49:35We've put this together in two days, which I think is pretty good.
49:39And the one critical thing is that the masts,
49:41which are the fundamental weakest point in the whole system,
49:44are working perfectly fine, even though the roof is three times as big.
49:49So who's right? Reiner or Chris?
49:53Although both experiments worked,
49:55ancient evidence tends to support Reiner's beam method over Chris's rope construction.
50:04The painting from Pompeii looks more like Reiner's roof than Chris's.
50:09And the beam construction has another historical advantage.
50:13According to ancient accounts, the Colosseum roof was retractable.
50:18In case of heavy winds or rain,
50:20the sailors who manned the awning would furl in the canvas,
50:24protecting it from the elements and lengthening its lifespan.
50:30This was easily accomplished with the boom design, but not with the rope roof.
50:36The main argument against Reiner's method
50:39is that it could never be large enough to cover the most important spectators at the Colosseum.
50:45But was this really a problem?
50:49As this computer reconstruction shows,
50:52a full-scale version of Reiner's awning would be a remarkably effective sunscreen.
50:58Over the course of a day, the sunniest seats would be on the north side of the stadium.
51:05But spectators seated on the south side, including the emperor,
51:08would find themselves in the shade all day long.
51:19It's not so easy.
51:22As a result of the reconstruction,
51:24Reiner is more convinced than ever that the Romans went with the beam method.
51:30You see, it's a convincing construction, I think.
51:33I think it's very near to what Roman spectators saw when they looked in the sky,
51:39in their amphitheatres. It's nice.
51:44I just think it's fantastic to think that the Romans ever built a roof over this building,
51:48because we've tried it with beams, we've tried it with ropes,
51:52and we know that it was difficult.
51:54And I think at the end of the day, you've just got to admire their achievement,
51:58because if you imagine this building, which at the moment is completely open to the sun,
52:02protected with almost like an umbrella over your head,
52:07it would completely change the quality of the space,
52:09and it would focus everything on what happens behind me here in the middle of this.
52:13I just think it's an amazing achievement.
52:17The Colosseum was the perfect expression of the brilliance and brutality that was Rome.
52:24And the giant canopy was its crowning glory.
52:28Floating above the crowds, providing comfort and shade,
52:33even as the bloody show went on.
52:48Now, log on to another lost empire, Ancient Egypt.
52:52At NOVA's website, navigate the tunnels, tombs and temples of the pharaohs,
52:56and follow a real-time excavation at Giza.
53:00Experience Pyramids, the inside story, on NOVA PBS Online Adventure.
53:23To order NOVA's Secrets of Lost Empires miniseries on videocassette,
53:27call 1-800-255-9424.
53:31This five-hour set is $69.95, plus shipping and handling.
53:35Individual programs are also available for $19.95 each.
53:52NOVA is a production of WGBH Boston.