Extreme Archaeology: Ancient Roman Bridge Hidden By Sinking Mud

All over Britain there are archaeological sites that are too dangerous to access or excavate. They could contain unique and valuable evidence of our past, which if not investigated will be lost forever. EXA is a team of highly skilled archaeologists. Katie Hurst in charge of excavation. Alice Roberts, doctor and expert in human bones. Meg Watters, geophysicist and digital imaging specialist. All experts in their chosen fields who are determined to get into these inhospitable places to forensically assess, survey and extract the evidence. The expedition leader will be me, Mark Davis, volcanologist, climber, caver and diver. This is archaeology on the very edge. This week we're in South Wales up to our knees in mud in the fast-flowing River Wye as we try to find a lost Roman bridge. This is Chepstow on the borders of England and Wales. It's also home to one of the greatest Norman castles we've ever known. Now I know this may look serene but welcome to the world of extreme archaeology. Meg, you're gonna have to get up. You gotta move mate. I think I need to move that way because my knee's this way. The Wye is a dangerous river. It's fast flowing and has the second largest tidal range in the world. The river can rise and fall by over 12 meters. That's 36 feet. At low tide the mud flats are deadly, sucking in anyone that dares step on them. 80 meters from the bank this mysterious structure of wooden posts appears on the English side of the river. It looks about two meters square and is believed to be the foundations of an ancient bridge. There's a chance it could be medieval but archaeologists and locals think it could be even older. A wooden Roman bridge, one of only 35 known in the world. Our mission is to get to the structure, extract a piece of timber and date it. If we can prove it's Roman and dating from the first century it will be the first evidence that the Romans crossed from England to Wales at Chepstow. It's high risk. We can only work at low tide for an hour twice a day. The mud is lethal and if we get stuck there's a real danger of drowning. It'll probably be really nice in winter. The team are preparing to take the direct route to the bridge foundation by walking to it through the mud. Lead archaeologist Katie has to work out an excavation strategy with Alice. Meg, our geophysicist, needs to see if she can get a radar kit down to the foundation. Over the last 2,000 years no one has ever got closer to the archaeology than this. Well, we're so close to the site and yet we've really got no more information. This could still be medieval, it could be Roman. I could plainly see the structure from here, I could see all the blocks and then the outer ring of it. Can you not determine from that whether it's Roman or medieval? We can see it, we could map it, we could get a position for it but we don't understand it yet. There's a number of possibilities there. I mean we can see structure, we can see what look like driven oak piles which is promising, that's potentially dateable material for us. But up here we might as well be a million miles away from there. Without getting right up close to it and getting samples from that material we're never going to resolve the question of what we're looking at. It's time for the team to set off. Sadly, I'm not going with them. But I will be on the end of a rope with the delivery team to drag them out if need be. I'm just going to get stuck in it. I know. Oh God. They're up to their knees and we're only about two, three meters down on the bank. It looks like it's going to get a lot worse from right now. They've only got an hour before the tide rushes back in and swallows the site. We're nearly there. Are you up to your weight? No, it's my thigh. It may seem like fun now but every step is sapping their strength. I'm in the situation you were in now Meg. Okay, come here. I'm getting concerned. It's over 80 degrees and even hotter in their dry suits. Okay, I really need to get my legs out. My leg is stuck. Come on, this is actually quite scary isn't it? By the time we get down here they're going to overheat in there and I don't think it's worthwhile. Let's get you out Alice, you're looking a bit hot to say the least. Meg, I'm going to get back. Slowly. Take it little bit by bit. Bit of slack. Mike, yeah. Mike. Pulling. Ow. It was actually quite scary. Yeah? Yeah, when I went down. I definitely do not want to be excavating down there. I've got things to do. It's like Mike was saying, calm down. We totally run. We've got to get these guys up. Go and get out of that suit. There's no way we can work in this mud. I can't imagine why anyone would want to build a bridge here. Why not at the most of the river? I mean, you're coming way up the river here. Why don't we build it down there? If you look at Roman sites located along these rivers, generally they're located up river. If you're right on the coast, you're exposed. You're vulnerable to storm, damage, or even attack from the sea. Position your bridge further upstream where you've got settled conditions, but as low down the river as you can so that navigable boats can come up to it. And this location is also away from that big cliff that the castle is located on top of. There's no way you can get a road on the other side there. Right. You need something where you can get access on both sides of the bridge for your road. If the Romans did build a bridge here, the mud or the tide wouldn't have put them off. Their legions were equipped with specialist bridge builders, pile driving machines, floating pontoons, and a plentiful supply of slaves. Meg? Meg, you're going to have to get up. You've got to move, mate. It's not a free meal ticket. With Alice safely out, it looks like Katie and Meg are exhausted. There's a real danger of being sucked in deeper. And it's... If I can dig this out, get down to my... Focus on getting Meg out. I'm sorry. Okay, can you not try and do step by step now? You're up to the really deep stuff, yeah? Let's just try giving you a tight rope and see what happens. Let's just try crawling in now. You ready? Yeah. The mud is just making everything impossible to grip. Okay. I was really scared. You know when you're on a beach? You have your feet and you wiggle your feet back and forth and suddenly you're up to your ankles in water. That's what they're experiencing down there. It's a process called liquefaction and it really is quicksand. Okay. That's good. Thank you. Yeah. Okay, should I... Oh, nope. Hold on, hold on, hold on. Come on, Meg. A little slack. Come on, Meg. Just a little slack. I'll get my feet under me again. How'd you find it, Meg? Well... Sticky. I don't know. I was really seriously... And my knee started really hurting. Your knee did? Did you twist it? Yeah, it was the wrong way around in the mud. So I couldn't stand up. Yeah, come a little further up. Well done. Trying to build a bridge over 200 meters long is a huge undertaking. The Romans must have had a pressing reason to get into Wales. It depends on the date of the bridge. If we're talking early on the first century, that's when the Romans are having to cope with a restless population. We're on a frontier at this time. The other side, Wales, is a restless guerrilla warfare population that's causing unrest in the part of Britain that they've occupied. So they may be building a bridge to provide them with the supply route they're going to need to supply that occupying army. Think later on, once we've got a settled, occupied Britain with the local populace settled into a Romanised way of life. In that situation, the road infrastructure, it's all about trade, about allowing armies and the civilian population to move around. So it's essential that we get a date for this structure. But on our first attempt, we've got nowhere near it. You're almost there. Katie's been in the mud for over an hour and the tide's about to turn. The risk of infection's high, but so is the risk of heat stroke. How was it? Exhausting. Just sit down. I know you wanted to go all the way out, but I just think it was just not worth the effort. Yeah, I don't think so. No? Do you think it's possible to go down and excavate? I don't know, we'd be so knackered by the time we even got there. Is it? And it's really quite frightening when you're up to your waist and you can't move. Yeah. And I don't want to be in a situation when the tide's coming up. I'm stuck there. The mud beat us this time, but we're not giving up that easily. We'll just have to think of another way of getting to the bridge. I think it's safe to say that it was a bit too difficult to get down there. Well, I don't know. It felt dangerous to me. I know it wasn't. I know that Mike and Trevor and you were looking after us, but no, it did feel a bit... I got a bit panicky down there, I have to say. Honestly, I don't think it's an option to go dig down there. I don't want to go back down with a bunch of equipment on me to go get stuck in the mud. Other ideas, I mean, we could put sort of crawl boards down. Yeah, that's all very well, but the problem is this is a site of scientific interest, so we can't put any structure down there because we don't want to damage this area. We also have the problem of the boards floating away at high tide. I think that's more of a problem. I think that's more probably going to lose them all. Even if they don't float away, we can't pull them back up. We have to leave this area as pristine as we found it. The way it is at the moment, we're going to come to this site and we're going to go away empty-handed. Yeah. We've only got six hours until the next low tide to think of a solution. We're investigating a possible Roman bridge in the River Wye, but we've got to wait six hours before the archaeology becomes accessible again. If there was a bridge here, it must have had a road leading up to it. Meg is going to use ground-penetrating radar to try and locate it. What we're going to try to do with the radar kit is actually find a road. We think we have a bridge or bridge footing, and what we're going to do is look for the road that would be associated with that bridge. OK, so your plan is what? To start where we saw the features in the mud? Well, I think what we're going to do, because we do have a feature that we are thinking is a footing of the bridge, is we're going to start right on the edge of the river and we're going to work our way up the field here. I know very little about geophys. I am learning all the time off Meg and basically just doing what she tells me, but I'm fascinated by it because as a doctor, I'm sort of seeing the similarities with things like ground-penetrating radar and techniques that we might use like ultrasound or MRI scans on people. When you actually sort of cut through people effectively, and what we're doing here is cutting through the ground and trying to get images of what's lying underneath the ground. With the radar data, you'll see when we start collecting the data, you see vertically into the ground, so we're like actually looking straight down with radar waves and it sees the differences in between different layers or rocks, stones, if they're voids, holes in the ground, or perhaps a Roman road. I can kind of see a structure in the ground. So give me an idea of scale, how wide is that across? If we start over here, where I start to see a layer, that's two, four, just about five metres. It looks about 50 centimetres down maybe, 75. Whereabouts? Right here. Okay. Please tell me you think it's a Roman road. Well actually, if you look at the box, three metres behind the box and then it extends about three to four metres off in that direction. Hey, that's wide enough to be a road. She's committed, you're not. It's beginning to look like a road, but Meg still has to track it another 20 metres up the field. If there was a bridge at this point over the Wye, it would have needed additional piers sunk deep into the mud to span the 200 metres of the river. So Katie's going to look for any possible remaining structures with the help of underwater archaeologist Mark Lawrence. They're going to use side-scan sonar to get an image of the riverbed. The scanner sends out sound waves that will reflect off any structures on the bottom. They're trawling over the centre of the river and are beginning to pick up some interesting images. What's this bit? Oh, that looks like... Can we pause that a minute? This is in the centre of the river. What that represents to me is sort of a depression with a bit of a build-up around the edge. It's not really a structure. It's not a big upstanding structure, no. If you like, it looks like a hole with a slight build-up of sediment around it, so like a mini cofferdam, if you like. It's actually very different from this structure here that we can see. That must be where the posts are, isn't it? I think that probably is. It's got a very flat face to it. There's no great elevation to it, but you can see that there's quite a different acoustic response in this area, so that material there is very different from the sediments that immediately surround it. But the shape itself is very strange because if you've got a square structure, I mean, that doesn't really suggest to me the base of a bridge because you would expect a lozenge shape to make it streamline against the tide. Do you think it's worth actually diving over that depression? Because we're never going to be able to see it otherwise, are we? The way the current is, the flow of the river is so fast. And look at the visibility. I mean, it's just, you wouldn't have any fun down there at all. What we can do is throw this camera in, I'll just, you know, see how bad the visibility really is. I can't even see your hand. It's so black down there. I can just see the shadow of your fingers. It's so bad. It may have been a murky survey, but this could be a bridge foundation in the middle of the river. Along with our feature in the mud and the early results from Meg's radar, all the evidence is pointing to a substantial crossing. Meg's field survey has found something six metres wide and 50 centimetres below the surface. Is this the road we are looking for? The only way to find out is to dig. Katie and Alice are just below the topsoil and they've already hit something. We've got a layer of limestone here that's really compact and it's looking as though it's some kind of surface. Great. Katie, do you think that looks like a Roman road surface then? It's very rough for a Roman road surface. It could well be later. I mean, we don't really know yet. So it could even just be where the farmers dumped some material. Because it gets a bit boggy down here, there's the river. And if it does look like a road, I mean, how would you date it? Well, what we really want is some pottery or a coin. Without any dateable finds, this road, if it is a road, could even be medieval. Meanwhile, the delivery team have come up with a novel solution as to how we get down to the submerged bridge foundation. I feel like I've stepped into a Star Trek movie with all this kit. But we are going to take our inspiration from another movie. The general plan is that we get the zip wire across at high tide so when it's low tide, you can lower the team down onto the site itself. Trev's got his kayak, they're both going to go across. Trev's going to paddle while Mike takes the rope and see if they can get across this wide stretch of river. It's high tide and Mike and Trevor have to drag over 200 metres of wet rope across to the Welsh side of the river. Meg's finished her survey of the field and is tying it into our GIS system. For example, we've got an elevation model here. This is the ordnance survey data which we can actually spin around. So you can really see it's a valley. It's a really pretty deep valley. You can see right along the valley here. Oh wow, that is terrific. And if we actually zoom right in and bring back the aerial photograph. I was going to say, can you put the photo on top? That's when it starts to get really exciting. OK. You can see the location. You can see the field where we've been, where we're based at the moment. You'll see now it starts. Oh wow, look at that in three, that's terrific. And have you actually put the survey data in here? What I had in the radar? Absolutely. Yeah, we can bring the survey data in and then from that, we can work out or estimate where we believe the bridge is going to be. At the moment. It's a nice straight line. Absolutely. And it's just an estimation at the moment. OK. From the road and Meg's data and our foundation in the mud, could this be the route the bridge took over the river? Katie and Alice are confident they have a road, but it just looks like they've uncovered a pile of rocks. It is a pile of rocks, but it's really looking like a proper archaeological feature now. I mean, we've put this, we've put this trench over Meg's survey results and what she's found is a long linear feature coming all the way down through this field. Yeah. Towards the wooden posts that we can see. So it's looking more and more like a road of some sort. So would this have been the original top surface for the road then? This isn't necessarily classic, what you'd expect in a pristine road though. No, it's quite a rough surface. But it's very shallow then, is it? Well, it's quite often very closely packed cobbles and you even get sometimes, you know, beautiful slabs laid down above the cobbles. A little bit like or equivalent to an asphalt layer on top of it. Exactly. Could this be a lower layer of it then? Could this be like sort of hardcore underneath? I think, you know, that's perfectly possible. I can see with the naked eye and let me just confirm that. Yeah, this is what we call oolitic limestone. What does that mean? There's little bits of shells that rock back and forth with a current and they accrete calcium carbonate on it and you get these little snowball effect type things. But the important point is that the nearest oolitic limestone that we've got from here is right over by Chepstow Castle itself. The rest of it is massive limestone with very little oolites in it. So I suspect that it's been brought in. It doesn't look much like a Roman road but then again, it doesn't look medieval either. We'll never confirm anything unless we find some date and evidence. Mike and Trevor have anchored the zipline on the Welsh side. The tide's turned and they're making their way back. They've only got two hours to rig and test the line. For the next couple of days, there are spring tides which means we'll have an extra 20 minutes of working time. The zipline has to be tensioned correctly. Even though it's stretched over 200 metres it's still got a breaking strain of up to two tonnes. So it should easily be able to take the weight of two members of the team. While the water is high, it may look easy but the tide still has to drop another 12 metres. We're on the banks of the River Wye in Chepstow searching for a lost Roman bridge. We found what looks like a road leading up to the river but we haven't been able to date it. The only other evidence is visible twice a day at low tide when this square structure of wooden posts appears. We think it's the remains of a bridge foundation. The team tried walking to it but failed. The river's too dangerous to dive in so there's a new plan. We're going to hang the team off a zipline stretched 200 metres across the river. It's not your normal archaeological practice. The tide has dropped 12 metres. The zipline's ready. The equipment is getting the final once over and Katie is being secured. But she's concerned. I'm feeling a bit nervous now. This rope is looking really high. When we get out there, you're going to take your weight off of this thing and unclip. You're then attached here to this anchor system. You're going to sit on the board and I'm going to lower you. We'll go through it as we go out there. I'll tell you which ones to unclip. OK, you're coming with me. I'm coming out there with you. I'm going to be above you at all times. Good, OK. We need to get a move on. It's quite reassuring. Let's get walking. Fine, just fine. Yeah. OK, all right, we're all yours. So this is the moment of truth. There's a deathly silence as we send in one of the delivery team, Mike, and also Katie down on the zip wire. And the idea is to get them over the feature that we want to excavate and then lower them down onto it while it's low tide. OK, actually, I might, if I can, take a photograph from here. This is the first time anyone has been this close to the foundation, so Katie's going to record it in detail. The timber posts look about two foot square, but we can only see the tops of them. We can only guess how deep they've been driven into the mud. Up close, this is a massive structure. The tide is at its lowest and everything seems to be going to plan. I feel a bit like a trapeze artist. Whoa! Can I just tell you I'm having a really bad day? OK. Why isn't it you out there? Why is it Katie? I would love to go out, but, you know, I don't do those things. I don't think the zip line would hold you there. Thanks, Meg. We know the mud surrounding the foundation is dangerous, but the centre of it is unknown territory. Katie could sink up to her waist if she steps on it. OK, excellent. Stop, stop. So far, so good, but Katie's careful not to put too much weight on the archaeology. It actually looks quite solid. Her first job is to measure and record the bridge foundation. Actually, it's really manoeuvrable. She's sort of moving around like a spider on top of the structure. Another 35 minutes and the foundation will be underwater again, but we need to survey it and get an exact global position. Meg! That thing that she's holding in her hand, like a bit of a wand, is a reflector. We call it a corner cube reflector. So Meg's firing a laser beam down from a reference point, and it gives you the azimuth. It tells you where it is exactly. So she's running around that structure and registering it, which has never been done before. No, that's amazing. First survey of that archaeological feature. OK, coming in again. I'm a bit worried about the time, actually. Yeah? How long have we got? Probably about half hour before it starts coming back in. Really? Yeah, yeah. Oh, I'm going to shout. Katie! You've only got about half an hour! I hate to hurry you, but we're really running out of time now. I'm kind of settled now. I'm ready. OK. Katie's trying to dig out the mud from around the post, so she can then cut a sample with a handsaw. How deep do these things normally go? I mean, there might be two metres down. Three metres, I think. Two metres? Yeah, there might be. I mean, I'm going to try and dig down as deep as possible, because the wood that's in the mud is going to be really well preserved. Right. I mean, we're concerned about not standing on the archaeology, but I suppose as long as you stand on it carefully and don't actually move any of the stones around. Yeah, yeah, yeah, absolutely. Yuck, with her hands, she had to be wearing gloves. Disgusting. The mud's so soft that it's easier for Katie to slop it out with her hands. Smells good? It smells lovely. Well, things appear to be going quite well, but the problem is the tide has turned now, so we have literally minutes before that entire feature down there will just be submerged in water. Things are floating away. We need sacks ASAP. We're about to fill with water. In fact, we just filled with water. The post is nearly under water. Sack's on. The plan is to protect the post with sandbags to stop the mud backfilling. I'm getting very wet. Are they coming? I've completely lost sight of the post now. OK, sack coming down. It's nearly up to my knees now in water, so come on. My hands are so slippery, I'm so muddy. It's coming in really fast. You can just see it covering up bits by bits. It's incredible. It is incredibly close. I don't want to damage the post because I can't see it now. Well, I think... Oh, Katie's sitting in the water right now. You see how fast that tide runs as it turns? God, it's really fast. Cut. This tide is really fast. Mike, can you get me out of here? We're going to need lots of bodies on this black rope. We can go on the other side, the other side of the tripod. Oh, that's better. Hello. What are you doing? What are we doing? Pull away! OK, well, the system seems to have worked, but the thing that shocked us all is how fast the tide came back in. One minute they were on the archaeology, the next minute the tide came rushing in. So it seems to have worked, but anyway. Cheers. Oh, God, I'm soaked. Katie, how did it go? Well, it was really hard because there's stones, there's really sharp stones jam-packed all around the post, so it's going to take a lot of effort to get down. Was you slopping back inwards? Mud was collapsing in. And when I got down to about that far, I've exposed about that much post, and you can just see a groove running down. The thing that took the most time then was basically doing the whole, you know... The survey, yeah. Survey of it and taking photos. Because next time I think I can go straight down in there. I can just lift the sack up, and then we're already down to where I got to. The river beat us again, and our next attempt will be even riskier. It's a spring tide tonight, so we'll have an extra 20 minutes at low tide. 20 minutes of valuable excavation time. It's now 3.30 in the morning, and it's low tide, and we've got another shot at getting the wood back out to prove once and for all that this is a Roman bridge. We're all extremely exhausted, so I think this is going to be the most dangerous part of our excavations. We're going to go out on the zip wire. I'm going to lower Katie down over the archaeology, and we're going to be there a little bit in advance now, because obviously last time, you know, we totally got caught out by how fast that tide came in. So we've decided that she needs an extra pair of hands down there. We can't put another person on the rope and send them down, so the only thing we can do is get somebody in with a boat. I think the best thing is if Trevor gets in in his kayak. And who's going with Trevor? I think we've decided Alice is going to go. Yeah. OK. And you're happy with that, yeah? Yeah, I'm happy with that. Yeah. The plan is for the kayak to slide 80 metres over the mud. Let's hope it makes it to the water. Go. Lucky, guys. Holy cow. Whoa, whoa, whoa. We've got a safety boat on standby in the river, just in case. All right. You can go. Oh, my, that's incredible. Right, come on, Katie, let's do it. Right, come on, guys, let's get up there. That was fantastic. Luck, Katie. This is our second zipline attempt. With just over an hour to go before the tide turns, every second counts. It's pretty eerie, I know. Nearly there. Nice launch, guys. Perfect. Watch out for the posts. Yeah, they're just to one side of them. The team's in place and finally ready to start work. Whoa, the sea just broke. You all right? Hold on a sec. I can hear him grunting and groaning. Yeah, he doesn't sound very happy. He doesn't sound too happy, you know. The crow's jammed on the rope. I think he's definitely got a problem, Bea. What does that mean, if a crow's jammed? It means I can't let you down. Oh. What's happened is that everything was running smoothly and we got down over the side and the board which Mike was sitting on has split. Whoa. Consequently, everything has been caught up in the pulley system. So we've lost about half an hour. I think Mike's now devised a system where he can take the weight of Katie off the pulley and start to lower her down again. It's absolutely frustrating because everything was running perfectly. The canoe was launched perfectly. The pulley system was working perfectly. And something as soft as a board split has now scuppered our plans to get that wood up. So it's not looking too good. Well, we finally managed to get Katie on top of the rubble that's encased in the wooden frame itself. We've probably brought...