"Secrets of Lost Empires: Colosseum"

PBS Airdate: February 12, 1997
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__: We now return to Secrets of Lost Empires. In this hour, the Colosseum, an ancient arena of stone and sailcloth? How was it done? Join us as we attempt to top a Colosseum.

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NARRATOR (KEACH): Nearly two thousand years ago, the Emperor of Rome presented his subjects with a new gift. It was a monument of unprecedented scale. A marvel of architecture and engineering achievement. A testament to the power and glory of Rome. The Colosseum. Today, it's one of the most famous buildings in the world. Thousands of tourists flock to this site each day, but few understand the true nature of this ancient wonder. Because the Colosseum was not a sports stadium. This was a theater of death. In 1961, Dino de Laurentis presented his vision of the Roman arena in the film epic "Barabbas." Elaborate sets, complete with artificial hills and lakes, and exotic animals from the far reaches of the empire were all part of the ancient spectacle. But in the early 1960's, Hollywood could not show the one thing that the ancient audience came to see: Blood. The blood of unarmed prisoners torn apart by wild lions. The blood of exotic beasts slaughtered for pleasure. And the blood of gladiators—trained to fight—to the death. For over four hundred years, the Colosseum set the stage for mass murder. One typical day in the amphitheater could feature the executions of thousands of men and animals. The Colosseum was carefully designed to host these spectacular bloodbaths. Stretching over six hundred feet end to end, and covering six acres in downtown Rome, the Colosseum could seat over 45,000 spectators. The huge crowds were systematically herded to and from their assigned seats through eighty numbered entrances and stairways. Inside, the gruesome show was performed on a giant wooden stage, covered with fine sand to absorb the ever-flowing blood. The floor timbers have now rotted away, exposing a labyrinth of underground tunnels, cages, and cells for the doomed prisoners. As the show went on overhead, armies of stagehands negotiated the narrow hallways with fantastic props, machinery, and weapons. There were elevators and trap doors, so that beasts and gladiators could make dramatic entrances up onto the arena stage. But the most amazing construction at the Colosseum had nothing to do with the show. It was designed purely for the benefit of the audience, to keep them calm and content as the violent spectacle unfolded below. It was a roof. Even in the sweltering summer months, spectators at the Colosseum could remain cool and comfortable, thanks to an enormous roof that extended over the seats and protected them from the scorching Mediterranean sun. But not a shred of the original roof has survived. And the Colosseum's most spectacular feature is now its biggest mystery. What kind of roof could have covered such a huge building? Even 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. The few large arenas that are completely enclosed, like the Houston Astrodome, are spanned only with the help of steel supports and lightweight plastic fibers. But without modern materials, how did the Roman builders complete their awesome task? The largest surviving ancient roof covers the Pantheon, a temple to all the gods. Here, the Romans produced an engineering masterpiece: a magnificent dome that soars a hundred and fifty feet above the floor. Although it looks lighter than air, the concrete dome exerts five thousand tons of pressure onto massive walls—20 feet thick. The roof of the Pantheon was an amazing achievement, but could the Romans have used the same technique to cover the Colosseum—a building that's four times as big? We asked structural engineer Chris Wise.

CHRIS WISE: If I was an engineer two thousand years ago, I think I'd be in trouble at this moment, because if the emperor asked me to put a roof across here, I'd be trying to be making a sort of technological jump from anything that we know the Romans ever did. And I could start with a flat roof, very simple, doesn't span very far, and it would need in a building like this a forest of columns which would just get completely in the way of the spectators. They wouldn't be able to see anything. Another solution would be to just try and increase the span a bit, by using their new material, concrete, and to make a longer beam. And that's possible, but again, it would still need a forest of columns, a bit further apart, and eventually it would get to the point where the concrete, which is very brittle, would just break. And it would just snap. So, what it needs is a technological jump. And the Romans had that. They knew about arches, they knew about domes. And the nice thing about an arch is that you use the material for what it really is best at, and that's just pushing one stone, or one piece of concrete against the next piece. And you can make an arch that might span about 45 meters, which is about how far they managed at the Pantheon. And in an arch, each of those stones is pushing against the next one, and just taking the load, very slowly and carefully from stone to stone down to the ground. I think it would be crazy to do a solution like that at the Colosseum. Although you could imagine it, it would end up looking like this.

NARRATOR (KEACH): A concrete dome over the Colosseum would require supporting walls 25 meters or 80 feet thick. And the whole roof would be high enough to enclose St. Paul's Cathedral, or a modern skyscraper 30 stories tall.

CHRIS WISE: I think they had no option. They had to go for a very light roof over the amphitheaters, because any permanent roof would have been crazy.

NARRATOR (KEACH): There is evidence to support Chris's idea that the Colosseum had a lightweight roof. This is an ancient painting from the lost city of Pompeii. At the very top of the picture, suspended above the city's arena, is what appears to be a large, billowing cloth canopy. Was this the roof that covered the Colosseum? A few ancient Roman coins bear the image of the great amphitheater. None of them show the roof, but they do reveal a series of lines protruding from the top of the monument. Historians believe that these represent large, wooden masts, which clung to the amphitheater's walls and supported a giant canopy, or awning, over the spectators. Architectural historian Rainer Graefe has been obsessed with the mysterious roof since he first heard of it 25 years ago.

RAINER GRAEFE: I got involved in the Roman tent roofs at the University in Stuttgart, and I got so enthusiastic that I forgot another doctor thesis I just had begun and worked at two or more even, and began this research.

NARRATOR (KEACH): To solve the mystery, Rainer examined amphitheaters throughout the Roman empire, including this well-preserved stadium in Nimes, in southern France. Joining Rainer is Chris Wise. A leading expert on modern lightweight roofs, Chris is intrigued by the possibility of an ancient Roman version.

CHRIS WISE: The thing that, the thing that I find is that—it's so difficult—when you, when you see an amphitheater, you just think that that's the finished thing, but I mean really, really, an amphitheater without an awning is like a man without any hair.

RAINER GRAEFE: Yeah. Very nice. Really.

NARRATOR (KEACH): Seventy feet above the pavement, Rainer leads Chris along the narrow, upper rim of the stadium to an important clue.

CHRIS WISE: So, what have you got here, Rainer?

RAINER GRAEFE: We spoke already about the masts holding the tent roof, and you can see very clearly the whole technique to hold the masts. They put in, in the top of the masts, corbels, heavy stones, sticking out.

CHRIS WISE: Right.

RAINER GRAEFE: And they pierced it. They made a hole in it, and down in the cornice, you see a second hole for the foot of the mast.

CHRIS WISE: Right. About two meters down.

RAINER GRAEFE: Two meters down.

CHRIS WISE: Three meters down?

RAINER GRAEFE: Two meters exactly.

CHRIS WISE: Right. It would have been very beautiful when they had all the masts up.

RAINER GRAEFE: Yeah.

CHRIS WISE: It's fantastic.

RAINER GRAEFE: You must imagine.

CHRIS WISE: How many masts for the whole ...?

RAINER GRAEFE: A hundred twenty masts around.

NARRATOR (KEACH): The mast holes at Nimes helped Rainer explain similar evidence found at the Colosseum itself. Here, a hundred and fifty feet above the ground, ornamental stones jut out from the stadium wall. Rainer is convinced that these were the brackets that supported the giant masts seen on the ancient coins. Up until now, historians theorized that the masts supported a giant spiderweb of ropes, which in turn held a cloth covering over most of the Colosseum. But Rainer has come up with an entirely new theory.

RAINER GRAEFE: But we do not know how long they were.

NARRATOR (KEACH): He believes that instead of ropes, the masts held horizontal wooden beams that projected over the seats and supported the broad sheets of the canopy. Rainer has had some trouble selling his theory to other experts, including Chris.

CHRIS WISE: —if you like the strength of the top of the Colosseum, for example, to see whether or not it could take the forces that this system would put onto it.

NARRATOR (KEACH): To see who is right, NOVA challenged Rainer and Chris to put their ideas to the test and reconstruct the lost roof of the Colosseum. Since the ancient stadium is off-limits for new construction, Chris and Rainer travel to the town of Barcarrota, in an area of southern Spain controlled by the Romans two thousand years ago. They set up shop in a fifteenth century bullring. Here, a team of experts will try to solve the mystery by building two different versions of the ancient canopy.

CHRIS WISE: We've got one or two things planned for this old building, a fifteenth century castle in Spain. What we're planning to do is to put down on the sides a couple of rows of corbels.

RAINER GRAEFE: These are a modern version of the old mast holders?

CHRIS WISE: It is modern, yes.

RAINER GRAEFE: In steel. Why did you change this detail?

CHRIS WISE: Well, because in the original Roman amphitheaters, obviously they would have put the stone corbels in as they were building the walls up, and we couldn't do that here without making an enormous hole into the wall. And so in the end, what we've done is make a modern equivalent which has the same load-carrying capacity, but made out of steel.

MIKE O'RORKE: OK! Lift it up! Up, up!

CHRIS WISE: The scale of this project is about half the size of the Colosseum. But it's still going to be a fairly tricky job, because the big poles that we're moving around weigh about half a ton each.

NARRATOR (KEACH): The team's first job is to build a makeshift crane that can lift the large masts to the top of the bullring wall. Joining the construction crew is Brian Austen. Once a high-wire walker, Brian is the largest supplier of circus bigtops in Europe. His expertise in rigging poles, ropes, and cloth has made him a millionaire.

CHRIS WISE: Do you use these in the circus, Brian?

BRIAN AUSTEN: We use the sheer legs just to erect our main masts, which are anything up to 80 feet.

CHRIS WISE: So, twice as long as this pole.

BRIAN AUSTEN: Yeah.

CHRIS WISE: Crikey.

NARRATOR (KEACH): Once the crane is in place, the team will attempt to lift the first mast 35 feet from the ground below.

BRIAN AUSTEN: Pretty good.

CHRIS WISE: This big pole is going to cantilever over the end of the wall there, hang down a rope, and we're going to pick up the first mast and lift it from the bottom up into position. And then we're just going to tip it up very, very gently, very easily, absolutely no problem, and lower it into the corbels. Piece of cake.

NARRATOR (KEACH): Brian's work at the circus has taught him the power of the pulley.

BRIAN AUSTEN: And now, put that peg through there.

NARRATOR (KEACH): The ancient Romans also recognized the mechanical advantage provided by this simple device, and they often exploited it in the lifting of heavy weights.

CHRIS WISE: Come towards the front.

NARRATOR (KEACH): Thanks to the pulleys, the first stage of the operation goes smoothly. But getting the five-hundred-pound mast to the top of the wall is only half the job. The team now has to rotate the mast into a vertical position and slide it down into the corbel. Although Brian designed the crane himself, he has a sneaking suspicion that it's not quite tall enough to lift the mast to its proper height.

BRIAN AUSTEN: Because I don't think there's enough height there, to get it high enough.

CHRIS WISE: It doesn't matter. Oh, it doesn't—if we move that, all we'll do is, is—oh, you think that, that—you think at the moment that that's the rope that we tied around the top?

BRIAN AUSTEN: I don't think we're going to lift it high enough for us to tilt that there to lower that into that corbel.

CHRIS WISE: Well, should we try it and see what happens?

MIKE O'RORKE: Yeah, we'll get as much purchase on this end as we can.

CHRIS WISE: Yeah, that's it.

MIKE O'RORKE: And then, we'll all come over and pull this way.

CHRIS WISE: Yeah. And we'll stabilize it with this thing.

NARRATOR (KEACH): Brian was right to worry. As they rotate the mast, it gets stuck at an awkward angle between the top of the crane and the bullring wall.

BRIAN AUSTEN: Yeah, we need to go up, now.

CHRIS WISE: Can you pull, can you raise—can you raise it? Can you raise it—now, use the crane to lift it, just a tad.

NARRATOR (KEACH): The team struggles to loosen the mast, but this puts too much pressure on the crane.

CHRIS WISE: Just a tad. Whoa, whoa, whoa! It's breaking! It's breaking.

BRIAN AUSTEN: No, no, no. We've got to go up a touch!

MIKE O'RORKE: We only need another foot.

CHRIS WISE: No, keep going, but very, very gently. Brian, keep out of the way, because just in case it goes.

NARRATOR (KEACH): With the crane threatening to collapse, Chris hopes to reduce the strain by gently easing the whole contraption to one side.

BRIAN AUSTEN: I wouldn't do that!

CHRIS WISE: OK, this way!

IGNACIO ARTEAGA: But if we want to move it, we have to —

CHRIS WISE: Just go slowly, go on. Don't pull it, don't pull it, don't pull it down! Don't pull it down.

NARRATOR (KEACH): The plan pays off. And with one last pull, the mast finally hits its target.

BRIAN AUSTEN: You're there.

MIKE O'RORKE: Yo, my man!

CHRIS WISE: Is it in?

MIKE O'RORKE: It's in!

CHRIS WISE: I'm still shaking, actually, because for a moment there, I thought the crane was going to snap and everybody just get, go over the edge with the timber. But when we freed it all up near the end, it then went in as sweet as a button.

MIKE O'RORKE: Lift! Lift!

NARRATOR (KEACH): With the mast in place, the next step is to hang the horizontal beam that will carry the awning out over the seats. Rainer got the idea for these wooden beams from the ancient painting from Pompeii, where the canopy seems to hang from rigid supports. The picture was important, but it was hardly a blueprint for a stadium roof. If long wooden beams were used, how did the Romans suspend them over the heads of the spectators? A possible answer came from an accidental discovery just outside the Colosseum. Historian Norma Goldman.

NORMA GOLDMAN: Now, just below us here on the road, when a utility line, a gas main had to be repaired, the repairmen dug into a camp that has been identified as the camp for sailors from Missenum. Now, Missenum is almost two hundred miles below us down on the Bay of Naples. What would a camp for sailors be doing here in the middle of downtown Rome, next to the Colosseum? Obviously, the sailors were needed to handle the rope and the cloth. And even more compelling as evidence is the fact that the Latin word for the awning, the sails, is the word "vela," the same word for sails on ships.

NARRATOR (KEACH): This replica of an ancient ship shows the basic design used by the Romans. The sail hung down from a horizontal boom that was suspended from the top of the mast. Rainer believes that when it came time for the Romans to build a cloth roof for the Colosseum, they simply multiplied the number of masts and hung the sails between the booms, side to side instead of up and down. Back at the bullring, Rainer needs some nautical expertise to rig his canopy. Owain Roberts if a lifelong sailor, boat-builder, and an expert on ancient ships. Using the Roman ship as a model, Owain simply hangs the boom off-center, so that once it's swung into position, it will project further out over the seats. Chris doesn't believe that the Romans used wooden booms. And when he's done helping Rainer, he plans to build a model of the roof that does without them.

CHRIS WISE: Well, let's turn it around and then fix it.

NARRATOR (KEACH): As a modern engineer, he works mostly with synthetic materials, and today, he's uneasy about putting too much pressure on the giant pieces of timber. CHRIS WISE: We have to be very careful with the mast, though, because we're forcing it in, we're forcing it in at the bottom, and also these top sections, as we're turning it around, the ropes have got to pivot around there. So, we have to just be careful.

RAINER GRAEFE: Yeah, yeah. Yeah, yeah.

CHRIS WISE: Well, the worst thing that could happen is the mast could either—there's a lot of force going down here now, as you can imagine. The mast could go through the corbel at the bottom. Of if it got really tightened up as we're swinging it around, we may put too much bending in the mast, and it could snap just at the level of the top corbel, just down under here.

OWAIN ROBERTS: The mast is rotating a little.

NARRATOR (KEACH): Unlike Chris, Owain has decade of experience with wooden masts and booms, and he's confident that the poles will bend, not break.

OWAIN ROBERTS: Yeah, that's good.

CHRIS WISE: OK. Whoa, whoa, whoa. Fantastic. Yie! It works.

NARRATOR (KEACH): Over the next day, four more masts and booms rise above the bullring, all with the rigging of ancient Roman ships. The next step is to hang the canopy, and sailor Owain has brought along several hundred square yards of canvas to do the job.

OWAIN ROBERTS: Let's open this up, and see if it more or less fits.

CHRIS WISE: What do you want? One corner each?

NARRATOR (KEACH): Norma Goldman joins the crew as they begin the task of attaching the canvas to the beams.

CHRIS WISE: Let's just see if we can get it up. Whoa, there we go.

OWAIN ROBERTS: That's it. Lovely.

NARRATOR (KEACH): The team is building a small-scale version of Rainer's awning that will cover just a segment of the bullring. Rigging the canvas should be simple. But they suddenly run into a major snag.

CHRIS WISE: That little hook there, or that loop, has got to go over the end of the beam. That goes on first, so that's slid along like that.

NARRATOR (KEACH): In the construction rush, someone forgot to attach a crucial rope to the end of the booms before swinging them over the seats. And without it, they can't rig the canopy.

MIKE O'RORKE: Yeah, but how are we going to get out there?

CHRIS WISE: How would they have done it on a, on a sailing ship?

RAINER GRAEFE: On a sailing ship, yes. They would not sit on it. It's too dangerous. They have ropes under it to stand on and can —

CHRIS WISE: A rope underneath?

OWAIN ROBERTS: What's this about footropes? Footropes weren't invented —

RAINER GRAEFE: Footropes.

OWAIN ROBERTS: Footropes. Yes, these ropes you're talking about here, they weren't invented until about 1600 AD, this is. This is 1600 years later than this. So I think you either need to get somebody out on top of this, walking along and then edging along, which is quite possible for somebody —

CHRIS WISE: They can still hang on with one hand, can't they?

OWAIN ROBERTS: Yeah, sure! They've got that rope there to —

CHRIS WISE: Would you do it yourself?

OWAIN ROBERTS: If I was about 20 years younger, yes!

MIKE O'RORKE: All right, let's try it, then.

NARRATOR (KEACH): Although the Romans would not have made the same mistake as our novice crew, the ancient riggers probably did need to get out to the ends of the booms for repairs. Construction supervisor Mike O'Rorke offers to play the part of an ancient mariner, as he attempts to deliver two ropes to the end of the pole—30 feet above the seats.

MIKE O'RORKE: The rope's going to twist at the end.

NARRATOR (KEACH): Mike volunteered with enthusiasm, but as he inches out into midair, he's having second thoughts.

MIKE O'RORKE: This is not a good idea. I'm coming back. I can assure you.

CHRIS WISE: We haven't cracked it then, because it was about 30 meters up in the air at the Colosseum.

MIKE O'RORKE: Yes. I mean, this is a big enough drop from here.

CHRIS WISE: All right, we've got you.

RAINER GRAEFE: I think we didn't plan it in the right way, that's all.

OWAIN ROBERTS: I also think that Mike isn't used to going out on a spar like this, and I think if we'd had a seaman who was used to it, he'd have probably walked most of the way and just fitted it over the end. He might have sat down at the last minute, but he'd have been quite happy on that.

MIKE O'RORKE: It's pretty scary out there, I tell you.

OWAIN ROBERTS: Yes, indeed. But you're not used to doing this. But I think a sailor, as I say, from that period, would wander out quite quickly, do it and get back in no time. But here, unfortunately, we can just, we'll have to use a ladder, won't we?

CHRIS WISE: They wouldn't have had a 30 meter ladder in Rome!

NARRATOR (KEACH): Just as the crew is ready to give up and use a ladder, Rainer remembers an important feature about the booms.

RAINER GRAEFE: But, what is for me new now, the importance of being able to swing the beams out and in. This, I didn't think about before.

CHRIS WISE: Yeah. But, also lower them. We know we can also lower them.

RAINER GRAEFE: Or lower them, yes.

CHRIS WISE: Now, just keep it, keep the load on it, keep the load on it. Got it? All right, here we go.

NARRATOR (KEACH): Because the booms are suspended from ropes, they can be maneuvered backwards, forwards, up or down.

CHRIS WISE: Can we have another man to help, help Rainer?

NARRATOR (KEACH): Here at the bullring, the quickest solution is to lower the boom.

MIKE O'RORKE: Down, down, down, down. Keep going, keep going. Whoa. That's it. That's it.

NARRATOR (KEACH): The ends within reach, the real job of rigging the canopy can finally begin.

NORMA GOLDMAN: Rings on the bottom.

CHRIS WISE: Rings on the bottom or the top?

OWAIN ROBERTS: All right, so take a corner over there, take a corner over here. That's fine, just more —

NARRATOR (KEACH): Owain has designed a complicated system of ropes and rings that only a sailor can comprehend.

OWAIN ROBERTS: —start threading these lines through again. Let me just tie a bowline on that, and then we've got everything pulling against each other, haven't we?

NORMA GOLDMAN: First, we have to fix this?

OWAIN ROBERTS: What I did was to shove it through there. You can see now why the rings are on top, so that the canopy will lie evenly and not drag across it.

CHRIS WISE: OK, stop. Outside team, outside team, pull.

NARRATOR (KEACH): With the booms loaded with the canopy, Chris relies on interpreter Ignacio Arteaga to coordinate the final raising of the roof.

CHRIS WISE: And again. Once more. And once more on this side. And once more. And now, tie them off. RAINER GRAEFE: This is the roof I imagined always to have been over the Roman buildings. And you see, some details are a bit rough. But as a whole, it's a very beautiful roof. It gives us a good impression of the old construction. It looks very similar to the roof shown of the famous wall painting of Pompeii. We have here the beams, and we have the awning hanging on the beams, with rings. It went around, was a circle.

NARRATOR (KEACH): Rainer's reconstruction gives us just a hint of how the magnificent canopy might have looked as it fluttered over the Colosseum. At the ancient stadium, wind and rain long ago dissolved every trace of wood, rope, and cloth that made up the giant roof. In fact, much of the building has been destroyed by two millennia of decay and abuse. Earthquakes toppled half of the stadium's limestone facade. And scavengers stripped away the marble benches and statues. The remaining shell of the monument only survives because of a unique and durable building material, developed by Roman engineers: Concrete. Concrete not only made up all the internal passageways and supports for the seats, but it also formed a massive foundation for the entire structure—40 feet deep. What made Roman concrete so special? The answer lies 150 miles south of Rome at the foot of the infamous volcano, Mount Vesuvius. Here, historian Norma Goldman found the Roman engineers' secret ingredient, on the beach.

NORMA GOLDMAN: The sand produced from the several volcanoes from this section of the Bay of Naples had an amazing quality. When workmen mixed it with lime, the powder became cement. And when they mixed cement with gravel or rubble—that's called aggregate—and water, they got concrete.

NARRATOR (KEACH): The Greeks first invented concrete, but their mixture could take years to harden. The Romans perfected the recipe by adding volcanic sand. The porous nature of the sand created a concrete that would set in record time. And Roman concrete had another useful quality.

NORMA GOLDMAN: It sets underwater. And the longer it sets, the harder it gets.

NARRATOR (KEACH): The Romans used this cheap and durable material everywhere. From the British Isles to the deserts of the Middle East, concrete fueled an explosion of monumental Roman construction. Back in sunny Spain, Rainer's canopy is a big hit with the local construction crew. But praise for the 20 foot wood-supported awning has not been unanimous.

CHRIS WISE: Yeah, but I mean, you just told me that half the seats—you know, not all, all of the day are they all in shadow.

OWAIN ROBERTS: That's right. So, people might have moved around.

CHRIS WISE: No, it's full. It's full. It's a very popular thing.

NARRATOR (KEACH): Rainer, Chris, and Owain do agree that the wooden booms that support the canvas could extend to about one hundred feet before breaking. But would this be far enough at the Colosseum? Although entrance to the Colosseum was free, the seating was strictly segregated. The worst seats were under the Portico, where wooden bleachers were set up for the poor—and for women. In the rest of the stadium, the marble seating was assigned to men, according to wealth and social status. The lower rows immediately surrounding the arena were reserved for Senators, Knights, and Rome's holiest of women, the Vestal Virgins. The emperor and his family had the best seats of all, in a private box directly above the stage. Chris believes that an awning that extended only a hundred feet from the masts would never reach the seats of the wealthiest and most important spectators.

CHRIS WISE: I can't see why a system like this, which only covers half of the seats in the Colosseum, is the method for the Colosseum. You know, why?

RAINER GRAEFE: You must imagine it's two thousand years ago that they did it. And when we read that they covered the auditorium of the Colosseum—we know it's a very huge space—we have the wish to cover it totally. But they couldn't do it. That's my opinion.

CHRIS WISE: They couldn't do it using this method. I think that there's another way of doing it, which—using, I mean, using the same materials, the same rope, the same timber for the masts, the same canvas. I think if we simply put up some masts and slung a rope from side to side, a little bit like a suspension bridge, like a modern suspension bridge, we would be able to, to carry the canvas significantly further than we would do with this.

MIKE O'RORKE: Come on! Keep going, out of the way.

NARRATOR (KEACH): Unsatisfied with Rainer's beam method, Chris now wants to build his own version of the ancient roof, relying heavily on a single material: Rope. Before Rainer came up with his wooden boom theory, most historians believed that the ancient canopy was held up by a spiderweb of ropes.

CHRIS WISE: We're just starting to lay out the very first segment of the rope system.

NARRATOR (KEACH): Although the theory has been around for a couple of centuries, no one has ever tried to reconstruct a working model of the rope canopy. And it's now up to Chris to figure out all the practical details.

CHRIS WISE: And this point here, it's going to be the top of the mast, the one we put up.

NARRATOR (KEACH): His first discovery? If rope were the main support for the roof, the Romans needed a lot of it.

CHRIS WISE: And then, back here, this point, is going to be tied to the end of the pole that we put up this morning.

NARRATOR (KEACH): Even for an arena half the size of the Colosseum, Chris's design will require a monumental four miles of the stuff. To support the ropes, Chris has erected several 40 foot masts, and local riggers are assigned the delicate task of delivering the necessary lines straight to the top.

CHRIS WISE: This is where the canvas goes under here, OK? Like that. Double, double, and then —

NARRATOR (KEACH): In theory, Chris's roof will work like a suspension bridge. One set of ropes is strung between the tops of the masts surrounding the arena. Spaced along these upper ropes, a series of vertical "drop" lines runs down and supports a lower set of ropes, that carries the canvas awning. But achieving the elegant simplicity of his plan may be more difficult than Chris imagines.

CHRIS WISE: We run the ropes loose —

BRIAN AUSTEN: Hang on, that ain't going to work. It just, it—we've got 10 meters there, so, and we've got eight meters here. We're already two meters short without tightening it.

NARRATOR (KEACH): Bigtop expert Brian Austen has some doubts about Chris's design.

BRIAN AUSTEN: We would need to have a set of pulleys on the ground here, which you could then pull up —

NARRATOR (KEACH): To complicate matters, there has been a delay in the delivery of supplies to the bullring. And there aren't enough pulleys to properly tighten the four miles of rope in the roof.

BRIAN AUSTEN: —bring the load down here, back through there —

CHRIS WISE: We haven't got a block and we haven't got the pulleys. We've got to do it with the equipment that we've got. So what we've had to do is invent a few ways of getting ropes through things with a minimum amount of friction.

NARRATOR (KEACH): Chris's determination is typical of his ancient predecessors. Roman engineers were constantly overcoming major obstacles with their innovative building techniques.

CHRIS WISE: Now, tie, tie. Give us that rope, and we'll tie it up here.

NARRATOR (KEACH): Their success was instrumental in extending Rome's power across two million square miles of territory, and into Spain. Just a few miles from the bullring lies the ancient city of Merida, once the capital of Rome's western-most province. Like dozens of other Roman cities, Merida features a showcase of civil engineering projects, complete with bridges, bathhouses, and extensive public water works.

NORMA GOLDMAN: Although Merida was built on a strategic site on a river, no self-respecting Roman hydraulic engineer would allow people to drink from that polluted river water into which all of the sewers of the city flowed. Nothing was too difficult for them, though, in finding a source of fresh water. They came out to higher ground, north of the city, and built two huge dams. This one, covered with granite, 45 feet deep. And from the dammed reservoir, water was then channelled through underground conduits, 12 miles toward the city, following the contours of the land. And where there were hills, they went through them. Where there were shallow valleys, they covered them with low aqueducts. And where there were deep valleys, they covered them with the high, arched aqueducts, so that the water could be brought to the city for bathing, for drinking, for the fountains. This is one of the few genuine Roman baths still in existence. I'm in the women's section, but there's an identical section right next door for the men. And the women came down, not only for bathing and for healing, they came down for social reasons, to gossip, to talk about the new blond German wigs that were coming into fashion, to talk about the vulgar play last night in the theater, and perhaps to arrange for the engagement of a 12-year-old daughter who was now ready for marriage. Another very extravagant use of that precious water from the reservoir could have been in this Merida amphitheater. For it is most unusual in having water-proof cement lining the surfaces of this depressed area. And what for? For water to have flooded the entire area and small craft or miniature boats brought in to reenact mock naval battles, and the condemned criminals or slaves who were put aboard fought to the death.

NARRATOR (KEACH): Back at the bullring, Chris is plowing ahead with his rope canopy. For his roof, Chris is using two and a half times as much canvas as Rainer's design. At the Colosseum, the same design would require over two hundred thousand square feet of cloth—enough to cover four football fields.

CHRIS WISE: I just realized, I just realized we've got to have the top rope above the bottom rope when we tie the canvas on. Otherwise, we won't be able to lift it through. So this, if this isn't, if this isn't above here, we can't lift it up when we finally do the —

NARRATOR (KEACH): Chris's enthusiasm for the project is not shared by the other members of the team.

CHRIS WISE: Sorry. Say sorry—sorry, guys.

IGNACIO ARTEAGA: Por favor, perdon.

CHRIS WISE: Thanks.

NARRATOR (KEACH): Brian is still troubled by doubts.

BRIAN AUSTEN: —and the masts are only nine and a half. Plus, the top rope then goes nine and a half meters above them, and there is no mast. So, we're nine and a half meters short on the masts.

CHRIS WISE: OK, for this one —

INTERVIEWER: Can you put that in simple English?

BRIAN AUSTEN: It isn't going to work.

CHRIS WISE: What isn't going to work?

BRIAN AUSTEN: We aren't going to get it up.

CHRIS WISE: Why?

BRIAN AUSTEN: Well, what we need to do at some point is to tighten the lower rope.

CHRIS WISE: Yeah?

BRIAN AUSTEN: And all the sails are connected around the back —

CHRIS WISE: Right.

BRIAN AUSTEN: So, they will have to either be untied, or they'll just get torn as we tighten it up.

NARRATOR (KEACH): Chris plans to raise the roof by tightening only the upper ropes. But Brian fears that if the lower ropes are left slack, the slightest bit of wind might set the roof flapping uncontrollably, and that could destroy the canvas.

CHRIS WISE: Yeah, I mean, it's not going to be perfect. But it would be perfect if we had the pulleys to adjust everything, but we haven't got them.

BRIAN AUSTEN: Yeah, but if we had the pulleys to adjust the back now, the sails are around the inside of the poles. So if you tighten the rope backwards, we're going to tear the sails.

CHRIS WISE: I'm not touching the, I mean, we're not touching that.

BRIAN AUSTEN: No, because we're not going to actually do it properly. We're going to end up offsetting it.

CHRIS WISE: It will work fine. It'll work absolutely fine. It'll look absolutely beautiful, believe me, by tensioning the bottom ropes over there.

BRIAN AUSTEN: OK.

MIKE O'RORKE: Start with, Ignacio, start with this first one. This end.

NARRATOR (KEACH): As the crew scurries to attach the canvas to the ropes, Rainer retreats to the top of the bell tower overlooking the bullring. With his bird's eye view, Rainer can see bad news for Chris on the horizon.

CHRIS WISE: Well, I would have been fine if we had been doing this three days ago, because it was completely flat calm. But over there is an enormous black cloud which is coming over, with wind, and behind me is a big sail, which eventually I hope will be a roof. And I'm, I think it will be OK. The most important thing is for, is just to explain to the guys so that they will know precisely what they are supposed to be doing and they don't pull out of sequence. We know that the wind will catch underneath the canvas and lift it right up. When that happens, just hang on, don't panic.

NARRATOR (KEACH): After two tedious days of looping, threading, and knotting, the four miles of rope and thousands of square feet of canvas are finally in place. And it's time to put Chris's theory to the test. CHRIS WISE: Owain, can you, can you take up the slack on that one?

NARRATOR (KEACH): In order to raise the giant canopy safely, four teams of men positioned at strategic points around the bullring must pull their ropes precisely on cue. CHRIS WISE: Can you go up there, please?

BRIAN AUSTEN: And then tell them to pull.

CHRIS WISE: Yeah. And we should lift?

BRIAN AUSTEN: Right.

CHRIS WISE: Owain, can you pull yours? Yeah, keep going, keep going, keep going, keep going. Mike, can you keep going on your side?

MIKE O'RORKE: Pull! Pull! Pull! Pull! Pull! Pull! Pull!

CHRIS WISE: OK, whoa! Tie it off.

NARRATOR (KEACH): Chris hopes the approaching wind will actually help lift the roof to its proper height.

CHRIS WISE: Starting from the end one, tighten up the top rope.

CHRIS WISE: But as the first gusts attack the awning, Brian senses trouble.

BRIAN AUSTEN: Yeah. You want to be getting it together now, or we're going to lose the lot. You will do, if you don't—you want to get it even now.

NARRATOR (KEACH): Just as he predicted, the lines holding the canopy are too slack and thrash violently.

BRIAN AUSTEN: He's got no tension on the bottom, and that's the opposing side to the lifting.

NARRATOR (KEACH): The canvas can't take the pressure, and starts to rip right off the ropes.

CHRIS WISE: Looks like it might self-destruct.

NARRATOR (KEACH): In an attempt to stop the billowing, Brian does his best to tighten the lower ropes that carry the canopy. Without any pulleys, it's nearly impossible to get the ropes completely taut. And Brian's strength and skill are all that's holding the roof together. Eventually, Brian's last-minute efforts pay off, and he's able to tighten the ropes just enough to stabilize the canopy.

CHRIS WISE: The interesting thing is, Brian has now stressed up the bottom ropes, and you can see it's started to stabilize. The rope structure itself is holding together very well.

NARRATOR (KEACH): As the windstorm subsides, the roof finally takes its intended shape.

BRIAN AUSTEN: The system itself is obviously one that does work, but the coordination in the erection kind of went to pieces. As soon as we got it up, we had no control over it, and as you can see, as I managed to coddle something together just to shorten the bottom, we get the true effect of what we set out to get.

CHRIS WISE: Yeah, I'm pleased. I mean, we've proved that it can be done. It's not perfect, but I think within the limitations of the time—we put this together in two days, which I think is pretty good. And the one critical thing is that the masts, which are the fundamental weakest point in the whole system, are working perfectly fine, even though the roof is three times as big.

NARRATOR (KEACH): So, who's right? Rainer or Chris? Although both experiments worked, ancient evidence tends to support Rainer's beam method over Chris's rope construction. The painting from Pompeii looks more like Rainer's roof than Chris's. And the beam construction has another historical advantage. According to ancient accounts, the Colosseum roof was retractable. In case of heavy winds or rain, the sailors who manned the awning would furl in the canvas, protecting it from the elements and lengthening its life-span. This was easily accomplished with the boom design, but not with the rope roof. The main argument against Rainer's method is that it could never be large enough to cover the most important spectators at the Colosseum. But was this really a problem? As this computer reconstruction shows, a full-scale version of Rainer's awning would be a remarkably effective sunscreen. Over the course of a day, the sunniest seats would be on the north side of the stadium. But spectators seated on the south side, including the emperor, would find themselves in the shade all day long. As a result of the reconstruction, Rainer is more convinced than ever that the Romans went with the beam method.

RAINER GRAEFE: You see, it's a convincing construction, I think. I think it's very near to what Roman spectators saw when they looked in the sky, in their amphitheaters. It's nice.

CHRIS WISE: I just think it's fantastic to think that the Romans ever built a roof over this building. Because we've tried it with beams, we've tried it with ropes, and we know that it was difficult. And I think at the end of the day, you've just got to admire their achievement. Because if you imagine this building, which at the moment is completely open to the sun, protected with a—almost like an umbrella over your head, it would completely change the quality of the space, and it would focus everything on what happens behind me here in the middle of this. I just think it's an amazing achievement.

NARRATOR (KEACH): The Colosseum was the perfect expression of the brilliance and brutality that was Rome. And the giant canopy was its crowning glory—floating above the crowds, providing comfort and shade—even as the bloody show went on.

__: Now, log onto another lost empire, ancient Egypt. At NOVA's website, navigate the tunnels, tombs, and temples of the pharaohs. And follow a real-time excavation at Quisa. Experience pyramids, the inside story. A NOVA PBS online adventure.

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__: Coming up on NOVA. When the best T.rex ever is found, everyone wants a piece of the action. The Feds. The Ranchers.

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__: Coming on The American Experience, it was the worst winter ever recorded. They were hopelessly lost.

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