The oldest bridge in the world ｜ Curators' Corner S10 Ep12

Ironically, we have spent the last seven years trying to save this bridge from water. This is factually the oldest known bridge in the world. This is not only a bridge, as it's often referred to, but it's in fact one of the most remarkable and mysterious hydraulic structures excavated in Iraq. It's emblematic of the Sumerian genius. They were able to master the water and that in turn led to the development of large urban centres. This bridge also tells us another story, the story of the collapse of the Sumerian civilisation as a whole. This hydraulic structure, as we see it today, is a beautiful ruin as well. It's a silhouette, it's this, I'm about to collapse but I'm not collapsing character. So whatever we do here, we want to keep it minimal, we want to just support it where necessary to protect and maintain its ruin character as well. Because that's what amazes all of us when we see the bridge for the first time. I'm Sebastian Roy, curator of ancient Mesopotamia at the British Museum and director of the Girsu project. My name is Ebru Torun, I'm an architect specialised in conservation. And that's how I got involved in the British Museum project to take care of the site of Girsu and especially our dear bridge here. Welcome to my corner. This unusual building that you can see behind me is entirely made of bricks and bitumen, measuring about 50 metres long, 30 metres wide, and as you can see it has a very unusual layout. It has an X-shaped plan more or less, like two main symmetrical walls that are supported with buttresses. These two ends actually are sitting on an exact north-south axis. As architects we always start with axis, you know, orientations and axis. So Sumerian architects also made themselves a nice north-south axis and placed the building accordingly. So this construction was excavated in the late 1920s, early 1930s by French teams working on behalf of the Louvre Museum in Paris. And it was excavated quite fast and with a lot of workers. So they exposed this firebrick structure, an immense structure, which they couldn't really identify the function of. Of course they came up with some interpretations, initially thinking it could have been a temple. They also thought it could have been a mausoleum, so a tomb, a royal tomb. Understandably because it's monumental and in archaeology mostly when you find firebrick structures of this scale it turns out to be a monument for a deity or for somebody important. It was mysterious from the start. And so they called it simply the enigmatic construction. After the end of the excavations in the 1930s, in the 1950s scholars went back to this construction and postulated that it could be linked to water. Now you might find this surprising because of course the site of Tello today looks like a desert. But in the past ancient city was a vast urban center with canals flowing around the site but also through the site. And so an ancient canal would have literally flown in between the two parts of this construction. In the early 2000s another scholar reinterpreted this construction and believed it could have been a bridge over this ancient canal. In 2016 when we started our new excavation project in Girsu, our aim was to first identify and excavate the ancient canal, confirm the function of this building to date the building properly and start a very important conservation program. Because after 80 years since the bridge was excavated when we found it in 2016 it was in a dire need of urgent conservation. Today archaeology possesses a number of tools. Drones, satellite images, geophysics, technologies that of course our predecessors didn't have. We had the suspicion, we had the hypothesis that in fact this structure was sitting on an ancient canal. So that was the first step. We flew a drone over the site of the bridge, identified the trace of this ancient canal and then we decided to excavate the canal. Archaeologists made trenches to the north of the structure to see whether we are going to hit actually stratigraphy of a canal and that's exactly what they found. I am in fact standing on this ancient dried up canal and you can notice that it is slightly raised above the surrounding archaeology. So just look at the workers behind me, they are much smaller than I am and if I take a few steps back I will fall five metres. The reason why this canal is preserved in this way is because the rain erodes much quicker the archaeological remains made of sun-dried mud brick than the very hard silt and sediment of this dried up canal. Over a number of seasons we were able to excavate the canal and prove that it was indeed contemporary with the construction itself. So what are we doing here and how do we approach this building, try to understand this building? Architects and archaeologists work together to understand the structure and architects and archaeologists working together is not evident, it is not a simple thing but here I think we found the right balance and while archaeologists are trying to understand not only the structure but also the context it is sitting in we architects are trying to understand, we are focusing on the building actually literally brick by brick every face of wall that we see the types of bricks, look at the joints in order to understand how it was maintained and changed through centuries and we approach this structure without any preconception without calling it a tomb or a temple or a bridge so what did I do? I said ok we are dealing with a structure built on a canal so we tried to find examples of historic buildings that we can compare it with which we failed, we didn't find any actually so I started to look at hydraulic structures today as we know them so you open a textbook of hydraulic structures and one of the first things you see next to dams and weirs and regulators you find a structure called a flume and the plan of a hydraulic flume today coincides exactly with what we have over here and of course even today when you constrict a wide canal, make it narrower in the middle of course it's very logical that you also span this canal with a bridge in fact in the middle we have foundation walls, three symmetrical foundation walls which must have carried a bridge now as you can see, the canal would have run in the middle of the bridge where it's the shortest span was the location of the bridge going up from east to west into the sacred city and the temple site of Girsu so one must imagine thousands of Sumerian pilgrims would have walked over the bridge across the canal and entered the holy city to try and date this building we opened a stratigraphic trench, so that's a step excavation which recalls all the archaeological layers, one on top of the others these layers are connected to the bridge itself so by dating the layers, in turn we were able to date the different construction phases of the bridge and so we were able to determine that the bridge in its current state, as you can see it today dates to the very end of the 3rd millennium or the very beginning of the 2nd millennium BC but we could also identify a precursor bridge dating back to the middle of the 3rd millennium that means roughly 4500 years ago so this is factually the oldest known bridge in the world this is not only a bridge as it's often referred to, like the oldest bridge in the world which is a very attractive way of calling it but it's in fact one of the oldest hydraulic structures that we know of 5000 years ago because what does the flume do? it actually funnels an existing body of water, passes it through a constricted area like squeezes it in the middle and lets it go downstream and that's very important because it tells us a lot about the way the Sumerians would have managed the water and this is emblematic of the Sumerian civilization as a whole this is why this bridge is important, it's symbolic it's emblematic of the Sumerian genius when all the water is collected to the north of the structure and passed through this narrow throat as they call it in fact it accelerates and the water level goes down, downstream what it also does, in fact doesn't do, it doesn't change the water level upstream which must have been very important in this region because agriculture depended on nicely calibrated water levels why would they need the water to flow faster? that's also very easy to understand because we are nearly level with the sea we know that water tends to stagnate here so you don't want your water in a canal to stagnate you want navigation, you want it to flow so I think it makes a lot of sense that they squeezed the canal to let it flow faster just like you would squeeze the mouth of a hose, you know, when you're gardening the research that we're carrying out here at the bridge feeds into another key question why a city like Girsu with perhaps 20,000 inhabitants suddenly collapsed after thousand years of existence and this collapse happened very quickly and it didn't only happen in Girsu many urban cities also were abandoned at that time we know that roughly at the time there is a change in the course of the Tigris river which shifts east and this has an important consequence on the entire networks of canals connected to the Tigris so there's less and less water flowing south towards the city of Girsu and so the genius of the Sumerian engineers were to build this structure, this sort of port of flume to accelerate the flow so that the water would continue to feed the different agricultural fields around the city so that they could continue to feed the population of Girsu so it makes a lot of sense to me but it also tells me which is something we have to work together with hydraulic engineers to study better that this may not be the only hydraulic structure of this nature we may find others in other cities because I do not know, for instance, how this acceleration was sustained perhaps they needed a second one, a third one because this canal actually reached the city of Nigin we know it from inscriptions it was a very important canal towards the end of the settlement here in Girsu so this structure was left to its fate for more than 80 years after it was excavated in the 1930s which meant that it was left in a very low basin in fact the lowest part of the entire site of Girsu which gets flooded completely after the winter rain and every time it rained, the basin would be filled up up to one meter or more with water so when we arrived here for the very first time about 10 years ago as you can imagine, after many decades of fieldwork interruption the construction was in a poor state of preservation some of the walls had already collapsed other parts of the bridge were just about to collapse and we had to start what we call emergency conservation so it was an immense challenge we had very little time trying to save this bridge from water so this brings us to the discussion of how to preserve this bridge and actually it's a very difficult task it could give an architect a kind of a panic attack, if I may say but of course, pulling up was one big problem so what did we do? we created a drainage system large pits, some pits, very deep, very large at the lowest part of the basin so we find the lowest part in the topography we create huge pits we fill them up with upside down boxes, plastic boxes actually to keep it all the time empty and make channels filled with gravel leading to those detention basins to divert the water away from our walls as much as we can so we have channels collecting the water between the buttresses they lead to a main channel and that main channel goes to a detention basin and we in fact create also a secondary drainage line at the base of the slopes that collects the water and the silt that's coming down from the slopes and we have the drainage channels at the base and we have succeeded, more or less, to keep the bridge dry and sometimes when it really rains very hard everywhere else is muddy and wet and full of water except the basin of the bridge, so I'm proud of that of course, it was very obvious that one of our main problems is water but just like a doctor would do with a sick patient we don't just immediately attack the first symptom we see but we try to understand the whole decaying process you know, the agents of deterioration and in fact the mechanism, the dynamics of deterioration we are at the east side of the bridge where we also have just started repair works you may wonder why the upper part of this wall is better preserved than the base one of the reasons here is that you may perhaps see a horizontal joint where the ancient builders used bitumen so it blocks the dampness here so in fact that means all the problems caused by the humidity is trapped beneath this joint because of the fact that this part was covered with soil in the past but when the excavations of the 1930s exposed the entire structure then this building started to have problems, of course because everything beneath this bituminous layer was then exposed and it's much more vulnerable from that moment onwards and that's due to the presence of soluble salts and water rising from beneath, from the water table soluble salts are transported with dampness and when the water evaporates those salts recrystallize within the bricks and within the mortar within the ancient structure and due to this crystallization they start to crumble, they start to break up so we're losing the original material if the salts are crystallizing within the original material and it erodes the bottom surface of the wall therefore here you see behind this protection plaster you still see the deteriorated part of the wall and where it's really badly damaged we inserted new bricks just to support the higher parts these are actually bricks that have more or less the same mechanical properties with the original bricks but they are more porous and therefore we hope to carry these salts to the surface but on the surface of the new materials that we're using and that's how we are hoping to protect and maintain this building in the longer term we are right under the bridge right now and we're doing our pointing and we're trying to understand the decay mechanisms also studying the existing materials and the way they behave this is how we find our walls this is a very dramatic example of basal erosion the upper part of the wall is still more or less in place I won't say intact but in place and you can see the deterioration process I was talking about that the water rises up, it's sucked up by the ancient wall and all the white you see over there are recrystallized salts that eat up our bricks so we are now cleaning to create ourselves a good base so that we can start building our conservation walls our walls that are going to support the hanging parts so this is the part we just started to repair but last season we worked on the northern extension wall so we are walking in the canal now this is the eastern wing wall and what you see here is a clear change in masonry because all this part was added later so this is the part we call the northern extension of the bridge because we realized studying the building that they had to extend the eastern wall because it seems the canal was trying to move a little bit the bed of the canal was trying to move a little bit eastward they wanted to stop the water circling around the hydraulic structure they wanted to again bring all the water back into the canal what you see here is the part we have repaired so you can see here the farshi bricks the porous spongy ones built to support the projecting parts of the ancient wall and here on the ancient wall you see old bitumen mortar and that's actually part of the problem the bitumen mortar can sometimes be part of our problem because you can see here that the basal erosion was really high really dramatic and we tried to understand why and the answer was at the other side of the wall because on this side all the joints are in bitumen mortar but at the other side we have mud mortar and only in intervals Sumerians used bitumen mortar and this line was the line of bitumen on the other side so all the water was actually trapped under that line and all the problems were accumulated all the basal erosion was concentrated beneath that bitumen layer but that also gave us the solution you know like actually I can't fight I can't stop this rising dam problem but I can contain it so what I do is we build this spongy wall as I say this porous wall so that all the sucked up humidity actually starts to evaporate from our wall you can see here already the salt crystallization on the surface of our wall but I use the same logic I put a barrier, a waterproof barrier between the new wall and the old wall so all the sucked up humidity is actually trapped in the new part it doesn't go further up in fact I have to credit my colleague Göze Göze Inar was the one who came up with the idea to put a water repellent barrier here so we are using the same logic the thing that we learned from the existing deterioration pattern we use it now in our favor to find a solution walltops are one of the most vulnerable parts of this structure at archaeological sites because it's continuously exposed to sun to wetting and drying cycles and we often see as we see here that the bricks slowly slide outwards one option and very conventional way of solving capping problems is adding more bricks adding several rows of bricks but here again architects have to step back and ask themselves what sort of an intervention can I make so that I don't lose the ruin value why do we love this building? why were we so impressed with this building? because it was such a beautiful ruin it was about to collapse but it doesn't collapse it's still holding on after so many thousands of years I don't want to ruin the ruin I want to keep it as a ruin but prolong its life at the same time so our solution was to use mud mortar basically so we create a new layer first with the synthetic netting and over it a thick layer of capping that actually holds the walltops together so you see behind me the east side is finished my colleagues are very busy with trying to finish the west side so these are actually the main interventions that we make our aim is to keep the significance of this building we want to prolong its life but we also want to respect its ruin character as well because that's what amazes all of us when we see the bridge for the first time so we're slowly approaching the end of the conservation project here and the big question in our minds is of course the future of this site how we can make sure that this site is protected but also is useful to different kinds of communities living here and in fact to the country of Iraq but it's very difficult as a foreign team to write up a site management plan that would involve government bodies and so on so we pick the parts that we can deal with, we can answer the basic one is to provide information in different ways so one of them is reaching out to the public like this but also we are very much aware that when we are here if we receive tourists we are enthusiastically explaining everything and everybody is impressed but we are only here for a couple of weeks so we need to leave behind information and for that reason we are now writing up panels in Arabic and English everything that I have explained you may be able to find it here when you come on the site that's the least we can do to leave behind but we also try to be useful to the communities around for instance I always think like our task is not only to serve the heritage here but heritage should perhaps serve the context that it's sitting in for instance we use the power of the site to make the roads better the communities here were complaining about how terrible their roads are every time it rained they were stranded kids cannot go to school we brought it up and we said if you want tourists we have to repair the roads and the first thing we could achieve we have a good road towards Girsu that's how I think the heritage should work together to match the problems of the communities the potential of the heritage can actually match the problems of the locality and we can actually find solutions that serve both purposes so that's our intention to leave behind a sustainably managed heritage site 2026 marks the 10 year anniversary of the Girsu project if you'd like to find out what they've been up to during that decade including using Sumerian mathematics to find the lost temple of Ningirsu and re-excavating a brick previously excavated by Alexander the Great then check out the playlist in the bottom left of your screen thank you so much it has been an absolute privilege