0:00:03 > 0:00:07Many people, many things have left their footprint on Wales.
0:00:07 > 0:00:11Some rugby players have landed with a pretty heavy tread.
0:00:11 > 0:00:16Some songs, and actors, and storytellers have left an indelible mark.
0:00:17 > 0:00:19Industry has left its scars.
0:00:19 > 0:00:25But the cutting edge of progress has also left behind the most memorable imprints -
0:00:25 > 0:00:32civil engineering, construction. They can sound a bit dry, but this is all about brilliance, genius.
0:00:34 > 0:00:39These now familiar landmarks were once pioneering projects,
0:00:39 > 0:00:42driven by the spirit of innovation, full of drama.
0:00:45 > 0:00:49Risks were taken, huge reputations were laid on the line.
0:00:51 > 0:00:55There were setbacks, grand plans were dogged
0:00:55 > 0:00:58by derailments, doubts, death and danger.
0:01:01 > 0:01:06Ultimately, there was triumph, all bearing the seal, built in Wales.
0:01:21 > 0:01:26For the first soaring achievement, we're going down, deep down.
0:01:29 > 0:01:31I've made this trip countless times,
0:01:31 > 0:01:35shuttling back and forth between my home in the borders and London.
0:01:38 > 0:01:42Overground rail travel, just for a few miles heading east out of Newport,
0:01:42 > 0:01:44and then suddenly...
0:01:47 > 0:01:48..underground travel
0:01:48 > 0:01:51into the black hole beneath the Severn Estuary,
0:01:51 > 0:01:54the watery divide between Wales and England.
0:01:56 > 0:02:01The Severn Tunnel. I know, it's a tunnel and there's not lot to see.
0:02:01 > 0:02:04But of all the feats of 19th-century engineering,
0:02:04 > 0:02:08this may well be the most dramatic. It took 13 years to build,
0:02:08 > 0:02:11is 4.5 miles long when it was completed in 1886.
0:02:11 > 0:02:15That made it the longest underwater tunnel in the world.
0:02:15 > 0:02:19Even if it had been built without a hitch, it would have been some tale.
0:02:19 > 0:02:22But this is all about what came at them unexpectedly.
0:02:22 > 0:02:26A force that has to be tamed to this very day.
0:02:29 > 0:02:33Today, there are other iconic crossings, over the Severn Estuary.
0:02:33 > 0:02:36Almost directly beneath is the Severn Tunnel,
0:02:36 > 0:02:40a project once dismissed as too risky and unpredictable,
0:02:40 > 0:02:43which it very nearly was.
0:02:43 > 0:02:46Building the tunnel ran into all kinds of difficulties.
0:02:46 > 0:02:51It's only here today because one man risked his life to save it from total flooding.
0:02:51 > 0:02:54More on Alexander Lambert in a minute.
0:03:00 > 0:03:03Before the tunnel was built, there was only a long, dangerous
0:03:03 > 0:03:07ferry crossing between New Passage in Gloucestershire and Portskewett in South Wales.
0:03:10 > 0:03:15Freight trains had to cross further upriver, at Gloucester.
0:03:16 > 0:03:18The original journey time
0:03:18 > 0:03:21from London to Cardiff via Gloucester was 5.5 hours.
0:03:21 > 0:03:24When the tunnel opened, it saved an hour and a quarter,
0:03:24 > 0:03:26so it went down to 4.25 hours.
0:03:26 > 0:03:29When the new line was built from Swindon to the tunnel,
0:03:29 > 0:03:32we saved another chunk of time, which brought us down to three hours.
0:03:32 > 0:03:36A tunnel is a black hole. Does that work against it?
0:03:36 > 0:03:39It's a tunnel and you don't see much of it, sadly.
0:03:39 > 0:03:44Therefore, it's never really had the high profile publicity
0:03:44 > 0:03:47that, say, the Forth Bridge or the Golden Gate Bridge
0:03:47 > 0:03:49in San Francisco has always had.
0:03:49 > 0:03:52You can look at the splendour and yet,
0:03:52 > 0:03:55the engineering that went into the Severn Tunnel was just as great.
0:03:58 > 0:04:04It was. Great Western Railway proposed tunnelling under the Severn Estuary at the Shoots,
0:04:04 > 0:04:08a relatively narrow stretch of water, but unusually deep.
0:04:10 > 0:04:16The tunnel would have to be forged through contorted and ever-changing strata of rock,
0:04:16 > 0:04:18200 ft below ground.
0:04:20 > 0:04:24And above it, the Severn Estuary, with the highest tides in Europe.
0:04:29 > 0:04:32And then there was always the notorious Severn Bore -
0:04:32 > 0:04:34tides and this wave.
0:04:34 > 0:04:38There was a constant danger of flooding.
0:04:42 > 0:04:45Digging the tunnel started in 1873,
0:04:45 > 0:04:48on the Welsh side of the estuary, here at Sudbrook.
0:04:48 > 0:04:51The site has been in constant use ever since and is still
0:04:51 > 0:04:55the tunnel control centre for the maintenance and monitoring teams.
0:04:55 > 0:05:00Experts, every one of them, in the workings of this underworld.
0:05:00 > 0:05:05The Victorian engineers started by sinking a shaft that went straight down 200 ft.
0:05:10 > 0:05:13To keep the workings dry, they built a drainage shaft
0:05:13 > 0:05:19that housed two engines, pumping out 300,000 gallons of water every day.
0:05:19 > 0:05:23That sounds an awful lot of water, but everyone thought that the two
0:05:23 > 0:05:27pumps were quite sufficient, until one day, when disaster struck.
0:05:34 > 0:05:37October 18th, 1879.
0:05:37 > 0:05:44The men working underground inadvertently tapped into a vast body of water stored in the rock.
0:05:44 > 0:05:47Nobody had known it was there.
0:05:47 > 0:05:50They called that they'd unleashed, the Great Spring,
0:05:50 > 0:05:54and it would be a source of anguish for years to come.
0:05:54 > 0:05:57In 24 hours, the entire works were flooded.
0:05:57 > 0:06:00Miraculously, no life was lost.
0:06:00 > 0:06:03The men working underground escaped with just a soaking.
0:06:07 > 0:06:12But the existing two pumps had no effect at all on the spring.
0:06:15 > 0:06:20300,000 gallons were nothing compared with the invading millions of gallons.
0:06:21 > 0:06:25They were six years into the project, everything came to a standstill.
0:06:28 > 0:06:33The Great Western Railway decided to hand over the project to a contractor.
0:06:34 > 0:06:38The man appointed was Thomas Walker.
0:06:38 > 0:06:42The new man in charge inspected the tunnel and found desolation.
0:06:42 > 0:06:45The shafts were flooded.
0:06:45 > 0:06:47Worse still, Walker was practically on his own.
0:06:47 > 0:06:52The work force had left to look for jobs elsewhere.
0:06:52 > 0:06:56Even with additional pumps, Walker found he couldn't get rid of the water.
0:06:56 > 0:07:02He decided what he had to do was isolate the flooded section, to give the pumps a chance.
0:07:02 > 0:07:06That meant sending in a diver, down the 200 ft shaft,
0:07:06 > 0:07:10along the tunnel, to get to a door that would seal off the flood.
0:07:10 > 0:07:15The man for this incredibly difficult challenge was one of the most famous divers of his day,
0:07:15 > 0:07:17Alexander Lambert.
0:07:24 > 0:07:27It was an extraordinary act of bravery.
0:07:27 > 0:07:30Lambert was working in the pitch-black,
0:07:30 > 0:07:34struggling through a tunnel littered with overturned skips.
0:07:34 > 0:07:38At any point, he could have ripped his hose and cut off his air supply.
0:07:43 > 0:07:45But that same hose was holding him back.
0:07:45 > 0:07:48He couldn't reach the door.
0:07:48 > 0:07:53So, Lambert went back down, with a brand-new piece of subaqua equipment.
0:07:53 > 0:07:59The latest version of the rebreather, recently designed by the inventor, Henry Fleus.
0:08:00 > 0:08:03The rebreather allowed the diver to be self-contained,
0:08:03 > 0:08:07but it had only ever been tested to a depth of 18 feet.
0:08:07 > 0:08:12Fleuss made the first attempt with it, here in the Severn Tunnel.
0:08:12 > 0:08:15But it was too much for him, and when he resurfaced,
0:08:15 > 0:08:18he swore that he would not go back down for anyone.
0:08:19 > 0:08:22So, down went Alexander Lambert again.
0:08:22 > 0:08:25This time, he did manage to close the door.
0:08:28 > 0:08:33Thanks to Lambert, the tunnel workings were soon clear, and work could at last resume.
0:08:36 > 0:08:38But more disasters followed.
0:08:38 > 0:08:42In 1883, a tidal wave swept up the estuary.
0:08:42 > 0:08:45Water poured into the workers' houses,
0:08:45 > 0:08:49the boilers and down the shaft, filling everything below.
0:08:49 > 0:08:52This time, one life was lost.
0:08:52 > 0:08:55The works were in a worse state than they had ever been.
0:09:00 > 0:09:03Once again, they pumped out the water.
0:09:03 > 0:09:06Once again, work resumed.
0:09:08 > 0:09:11The Great Spring continued to force its way through.
0:09:11 > 0:09:16By 1885, it had been sealed off by drawing it into a side tunnel.
0:09:17 > 0:09:21At last, the final section of the tunnel was completed
0:09:21 > 0:09:23and it was close to opening.
0:09:24 > 0:09:26Tunnel expert David Abenheimer
0:09:26 > 0:09:31is impressed by the scale of the work that once went on here.
0:09:31 > 0:09:37At its peak, Walker had 3,000 men working for him on the tunnel.
0:09:37 > 0:09:41The logistics of that were such that he formed,
0:09:41 > 0:09:44founded the village of Sudbrook at this end of the tunnel,
0:09:44 > 0:09:49just to provide accommodation for workmen and their families.
0:09:49 > 0:09:53He didn't just provide housing, he provided a post office, telegraph,
0:09:53 > 0:09:55a Mission Hall, a school,
0:09:55 > 0:10:01and he was very good in terms of providing for his workforce.
0:10:03 > 0:10:08In the autumn of 1885, Thomas Walker left for South America on a different project,
0:10:08 > 0:10:11exhausted, glad to leave this one behind him.
0:10:11 > 0:10:15He wasn't gone long. Within weeks, he received a telegram.
0:10:15 > 0:10:19The Great Spring was back. Sealed off, it was exerting
0:10:19 > 0:10:23such a force on the tunnel that bricks were beginning to shatter.
0:10:23 > 0:10:28Pieces were flying out of the wall and water was pouring through the gaps.
0:10:36 > 0:10:39Walker and Hawkshaw realised that the only real answer
0:10:39 > 0:10:42was to divert the Great Spring once and for all.
0:10:42 > 0:10:44This giant pumping station was built.
0:10:49 > 0:10:53The new building housed six massive Cornish beam engines that would pump
0:10:53 > 0:10:57the spring water from a catchment point underground to the surface.
0:11:00 > 0:11:02The six engines were beasts.
0:11:02 > 0:11:07Fed by eight boilers, they worked solidly round the clock.
0:11:08 > 0:11:13Nothing like them had ever been built anywhere in the world.
0:11:13 > 0:11:16The Great Spring had finally met its match.
0:11:29 > 0:11:32The culvert takes the spring water to a catchment point
0:11:32 > 0:11:36where the water is pumped all the way up those 200 ft to the surface.
0:11:40 > 0:11:45The original Cornish beam engines were replaced in the 1960s by these electric pumps.
0:11:45 > 0:11:50And on they go, just like the old engines, constantly pumping away,
0:11:50 > 0:11:52keeping the tunnel operational.
0:11:59 > 0:12:02Most of the water now gets pumped into the Severn Estuary.
0:12:02 > 0:12:05Welsh Water does take off a certain amount.
0:12:10 > 0:12:14With the Great Spring tamed at last, the tunnel was ready to open.
0:12:14 > 0:12:19It happened on 1st September, 1886, with no great ceremony.
0:12:19 > 0:12:22Perhaps nobody wanted to celebrate too soon.
0:12:25 > 0:12:28The story of the tunnel was to have a happy ending.
0:12:28 > 0:12:33Over 120 years later, it is in use as much as ever,
0:12:33 > 0:12:38the most important section of all the railway lines that connect Wales and England.
0:12:38 > 0:12:43Should we applaud the tunnel because it's still very much a working project?
0:12:43 > 0:12:48I think so. I think, what makes us applaud it is the fact that it took
0:12:48 > 0:12:52100 years for it to be surpassed by something like the Channel Tunnel.
0:12:52 > 0:12:58It stayed one of the longest tunnels, and the longest railway tunnel in the country for 100 years.
0:12:58 > 0:13:03- You're Welsh, does it have a special place for you?- Absolutely.
0:13:03 > 0:13:06If you don't keep the Severn Tunnel open,
0:13:06 > 0:13:10and if the pumps fail and it gets flooded...
0:13:12 > 0:13:15..England gets cut off from civilisation.
0:13:19 > 0:13:23There it is, the tunnel, a little black hole on the edge of Wales.
0:13:23 > 0:13:26There's something about this place, something chilling.
0:13:26 > 0:13:31All the major characters of its construction were dead within six years of its completion.
0:13:31 > 0:13:36They say it's haunted, but there is something far less chilling.
0:13:36 > 0:13:41There's not much to see from here or from the train, but down there it is an absolute masterpiece,
0:13:41 > 0:13:45and the spirit of Hawkshaw, Lambert and Walker lives on.
0:13:53 > 0:13:59For the next feat of engineering, I'm going from the depths of South Wales upwards to North East Wales...
0:14:02 > 0:14:06..and back further in time to the year of the Battle of Trafalgar
0:14:06 > 0:14:08to 1805 when this opened.
0:14:09 > 0:14:15Even when set against what can be built today with steel and concrete, it stands its ground.
0:14:15 > 0:14:21When it was first built, it set new global standards for length and height.
0:14:21 > 0:14:24But never mind the records, this is simply stunning,
0:14:24 > 0:14:29a combination of stone, metal and water, man-made elegance straddling a beautiful valley,
0:14:29 > 0:14:33a masterpiece, and not just for its majesty,
0:14:33 > 0:14:39but also because this was an early expression of a daring new spirit.
0:14:39 > 0:14:44This is the Pontcysyllte Aqueduct soaring over the River Dee in North Wales.
0:14:44 > 0:14:49When it was built just over 200 years ago, it was like no other structure on earth.
0:14:49 > 0:14:53It broke records, and people came from all over the world to admire it.
0:15:00 > 0:15:04Today, Pontcysyllte serves the tourist trade,
0:15:04 > 0:15:08catering for leisure barges on the Llangollen Canal.
0:15:08 > 0:15:11But the aqueduct was built for a different purpose.
0:15:15 > 0:15:20When work started in 1795, Britain was in the grip of canal mania.
0:15:20 > 0:15:22A time when 1,000 miles
0:15:22 > 0:15:26of new waterway was completed in just 20 years.
0:15:27 > 0:15:32Canals were the arteries of the Industrial Revolution.
0:15:34 > 0:15:39The Pontcysyllte Aqueduct was built as part of the Ellesmere Canal project,
0:15:39 > 0:15:46a 68-mile waterway network that would take Wales's mineral riches down into the Shropshire lowlands.
0:15:49 > 0:15:52The canal started on the Cheshire Plain.
0:15:54 > 0:15:58'In the Vale of Llangollen, it had to cross the River Dee.'
0:15:58 > 0:16:00This is the landscape they had to cross.
0:16:00 > 0:16:04Picturesque for us, but for a canal builder, full of challenges.
0:16:04 > 0:16:09The biggest obstacle they had to overcome the broad, deep Dee valley itself.
0:16:09 > 0:16:13Pontcysyllte translates as "the bridge that connects,"
0:16:13 > 0:16:17and that's exactly what it does, striding across the valley.
0:16:20 > 0:16:23In the numbers game, and in construction they always count,
0:16:23 > 0:16:26the following are revolutionary dimensions.
0:16:26 > 0:16:32The aqueduct is 126 ft high and 1007 ft long.
0:16:35 > 0:16:41It consists of 18 pillars that carry a cast iron trough that is 11 ft wide,
0:16:41 > 0:16:47wide enough, just for one canal boat to cross at a time and a toepath.
0:16:49 > 0:16:55The engineer appointed to oversee the project was William Jessop.
0:16:55 > 0:16:59Jessop was the most famous canal builder in Britain
0:16:59 > 0:17:04and he was well known for his modesty and his generous nature.
0:17:04 > 0:17:08The appointment of the resident engineer was, however,
0:17:08 > 0:17:10a more surprising choice.
0:17:12 > 0:17:16This was a 36-year-old Scot called Thomas Telford
0:17:16 > 0:17:20who had considerably less experience in building canals.
0:17:22 > 0:17:28But Telford was gifted and ambitious and this was his big chance.
0:17:28 > 0:17:32He was born to a shepherd, he was lucky enough to get an education.
0:17:32 > 0:17:36He worked as an apprentice stone mason in Scotland, but was one of those people with get up and go.
0:17:36 > 0:17:40When Telford got the job, as a young man on Ellesmere Canal,
0:17:40 > 0:17:43he wrote was very excitedly to his friend in Scotland,
0:17:43 > 0:17:50"I am engaged in the most noble enterprise in this country. It will be a great and wonderful thing."
0:17:50 > 0:17:56He was terribly excited in being part of this whole new world that was transforming Britain.
0:17:56 > 0:18:01This was the opportunity. 1793 was a boom year, canals being built
0:18:01 > 0:18:04all over Britain and this wasn't really the greatest at all.
0:18:04 > 0:18:07The thing that made this great was Pontcysyllte,
0:18:07 > 0:18:11nothing like that had ever been seen before and it made his name.
0:18:11 > 0:18:15Canals nowadays are enjoyed at a more leisurely pace.
0:18:15 > 0:18:17What were they in those days?
0:18:17 > 0:18:21The canals were the motorways of the age.
0:18:21 > 0:18:24Somebody did a calculation -
0:18:24 > 0:18:28if you want to carry goods and you put them on a packhorse,
0:18:28 > 0:18:31it could carry something like an eighth of a ton.
0:18:31 > 0:18:34The best you could do with a horse and cart
0:18:34 > 0:18:37on a really good road was about half a ton.
0:18:37 > 0:18:41Put the horse in front of a canal boat and it could move 30 tonnes.
0:18:41 > 0:18:44It was a huge increase in efficiency.
0:18:44 > 0:18:47It is fair to say that without the canals to move goods around,
0:18:47 > 0:18:52and particularly coal, we would not have had the Industrial Revolution in Britain.
0:18:56 > 0:19:01Telford was appointed engineer to the canal in 1793.
0:19:02 > 0:19:07The problem of how to cross the vast Dee Valley was still unresolved.
0:19:09 > 0:19:14At one point, it was agreed the aqueduct should cross the valley at a much lower level
0:19:14 > 0:19:18and barges would have to go up and down through a series of locks.
0:19:20 > 0:19:24But Telford saw flaws in the plan and ruled it out.
0:19:26 > 0:19:30Anyway, he had in mind something far bolder.
0:19:32 > 0:19:35This was the era of the picturesque.
0:19:35 > 0:19:39What man added had to enhance the landscape.
0:19:41 > 0:19:45What made Telford's design even more daring
0:19:45 > 0:19:49was its use of a new material still in its infancy...
0:19:51 > 0:19:52..cast iron.
0:19:52 > 0:19:56Its lines now look so classically clean and simple.
0:19:56 > 0:19:58Just how radical was this?
0:19:58 > 0:20:02Very radical, because the earlier aqueducts in Britain
0:20:02 > 0:20:04had been very low and squat.
0:20:04 > 0:20:09The waterproofing in them was a great mass of puddled clay,
0:20:09 > 0:20:13that's clay been treddled by navvies walking on it.
0:20:13 > 0:20:16So an enormous, heavy structure
0:20:16 > 0:20:20which couldn't reach the heights of the aqueduct here.
0:20:20 > 0:20:25So they were thinking of building a much lower structure until they got the ideas sorted out.
0:20:25 > 0:20:29- A lot of those ideas, did they revolve around cast iron?- Yes.
0:20:29 > 0:20:34In the age of Merthyr Tydfil, as the world centre of iron smelting,
0:20:34 > 0:20:40these huge fuel furnaces could actually produce enormous masses
0:20:40 > 0:20:44of cast-iron which could be used to build a large structure like this.
0:20:44 > 0:20:50It's so light that they could achieve these very high structures for the first time.
0:20:50 > 0:20:54Cast iron, how did it compare with what had been used before?
0:20:54 > 0:20:58It is extremely light compared to Roman aqueducts like Pont du Gard
0:20:58 > 0:21:01in southern France, which is about as high as this.
0:21:01 > 0:21:05But the stone sides of that are 4 ft thick.
0:21:05 > 0:21:09Here, with cast-iron we only needed plates which are an inch thick
0:21:09 > 0:21:12on either side, so it gives you some idea of the huge saving
0:21:12 > 0:21:18- in weight that cast iron enabled.- So we have this trough, 1,000 ft long.
0:21:18 > 0:21:20Did they have to do anything to stop it leaking?
0:21:20 > 0:21:26This was an example of one of the first uses of iron cement, but it was specialised cement because
0:21:26 > 0:21:33it was mixed with boiling ox blood, Welsh flannel and iron filings!
0:21:33 > 0:21:36That compressed together and...
0:21:36 > 0:21:43formed a watertight bond, and that's held and not really leaked significantly in 200 years.
0:21:43 > 0:21:47There must have been some trepidation on Telford's part.
0:21:47 > 0:21:50Here he was a relatively inexperienced canal engineer,
0:21:50 > 0:21:53pushing for a cast iron trough,
0:21:53 > 0:21:571,007 ft long, supported on stone pillars.
0:21:57 > 0:22:00It had never been done before. Would it work?
0:22:00 > 0:22:02The number of spans was set at 19,
0:22:02 > 0:22:07with 18 stone piers supporting the cast iron trough.
0:22:08 > 0:22:12These vast, stone piers, believe it or not, are partly hollow.
0:22:12 > 0:22:16It was another of Telford's brilliant ideas and became one of his trademarks.
0:22:16 > 0:22:20Solid stone piers to this height would have been too heavy.
0:22:20 > 0:22:25So, for about two-thirds of the way up, they are hollow and they taper
0:22:25 > 0:22:28and that's what's makes the whole thing so light and graceful.
0:22:41 > 0:22:46Peter, there is a modern buzz about this place, but how different was it, say, 200 hundred years ago?
0:22:46 > 0:22:50It would have been very different. This canal was built for commerce,
0:22:50 > 0:22:55there were coalmines, ironworks and brickworks, slate works,
0:22:55 > 0:23:00the chemical works coming in. This would have been a hive of industry activity 200 years ago.
0:23:00 > 0:23:03That's why the canal had to get across the valley to reach it.
0:23:03 > 0:23:08So this Scotsman says, "I will give you something very graceful to fit into this industry."
0:23:08 > 0:23:13- How did that go down?- Telford and Jessop, the senior engineers on this project, there is evidence from
0:23:13 > 0:23:16their writings and the records of the day, they were very conscious
0:23:16 > 0:23:21they were building a fantastic structure. It would be the tallest structure of the modern age.
0:23:21 > 0:23:28They needed to build something that would be beautiful rather than just plain and ordinary.
0:23:30 > 0:23:34Telford had begun his career as an apprentice stonemason
0:23:34 > 0:23:38and the quality of the stonework on all his projects was notable.
0:23:42 > 0:23:47The stone was just as important as his revolutionary cast-iron.
0:23:48 > 0:23:51The blocks for his aqueduct were quarried nearby.
0:23:51 > 0:23:56Each one of these vast blocks would have been hand-dressed on site.
0:24:01 > 0:24:04This etching was made during construction.
0:24:04 > 0:24:09It gives an idea of the height at which the stonemasons had to work.
0:24:11 > 0:24:16From the very outset, Jessop was worried about the safety of the stonemasons.
0:24:16 > 0:24:21In 1795 he wrote to Telford, "I foresee some difficulties
0:24:21 > 0:24:23"that appear to me formidable.
0:24:23 > 0:24:26"In the first place, I see the men giddy and terrified
0:24:26 > 0:24:30"in laying stones with such depth underneath them
0:24:30 > 0:24:35"with only a space of six feet wide and ten feet long to stand upon."
0:24:37 > 0:24:39The men would have been working right up there,
0:24:39 > 0:24:43without any scaffolding as we know it, no safety harness.
0:24:43 > 0:24:46One man did fall to his death. But that, according to Telford,
0:24:46 > 0:24:49was due to carelessness on his part.
0:24:49 > 0:24:53That sounds a bit cavalier, but Telford WAS concerned about safety.
0:24:53 > 0:24:58And you only have to compare that one single fatality with what happened, say, on the Forth Bridge
0:24:58 > 0:25:03built almost 100 years later. It's thought as many as 98 men died on that project.
0:25:11 > 0:25:14It's only when you're travelling across the aqueduct
0:25:14 > 0:25:18that you realise quite how dangerous it must have been for the workmen.
0:25:27 > 0:25:30Standing on the canal boat, on one side there's a frightening drop.
0:25:30 > 0:25:32Why's there no safety rail?
0:25:32 > 0:25:35One wasn't required. When this was a working canal,
0:25:35 > 0:25:39you'd have had a man leading a horse on the towpath, where there IS a rail for safety.
0:25:39 > 0:25:42There would have been just one person on the back of the boat.
0:25:42 > 0:25:46There would've been no question of them thinking about throwing themselves off
0:25:46 > 0:25:51so a safety rail wasn't needed. And iron was an expensive material, so they would have saved £100,
0:25:51 > 0:25:57which would have been a lot of money then, by not installing one. And we've never needed one since.
0:25:57 > 0:26:02It was all about industry. But can you give us some idea of the tourism it spawned back then?
0:26:02 > 0:26:04Remember, this is 1805 when it opened.
0:26:04 > 0:26:07We were at war with the French and half of Europe.
0:26:07 > 0:26:12So people couldn't go on the grand tour around the Renaissance sites that they would normally do.
0:26:12 > 0:26:16And so there was a kind of mini grand tour going on in Britain.
0:26:16 > 0:26:21So this landed at exactly the right time to attract the attention of the well-to-do.
0:26:21 > 0:26:23It had the wow factor when it was first built.
0:26:23 > 0:26:26People came from all over Britain and the modern world
0:26:26 > 0:26:28to look at it and marvel at it.
0:26:28 > 0:26:33And I think it's still got that today, even with the age of jets and motorways.
0:26:33 > 0:26:38You can still come here and stand on top of it or stand down at the river and look up at it, and be amazed
0:26:38 > 0:26:41that we've got the capability to build structures like that,
0:26:41 > 0:26:44that still look graceful and beautiful as well.
0:26:45 > 0:26:48In all, it took ten long years to build this aqueduct.
0:26:48 > 0:26:52But I think everyone involved knew they were working on something very special.
0:26:52 > 0:26:57It opened with a grand fanfare on the 26th of November 1805.
0:26:57 > 0:27:01Thousands of people gathered to cheer a small procession of boats
0:27:01 > 0:27:05going across. Telford was here to join in the celebrations.
0:27:05 > 0:27:07He didn't mind a bit of publicity.
0:27:07 > 0:27:12But it must have been an incredible occasion for him to stand alongside his stream in the sky
0:27:12 > 0:27:16that was about to become one of the wonders of the industrial world.
0:27:30 > 0:27:33What did this lead to in the world of aqueducts?
0:27:33 > 0:27:37Well, after this, people were inspired by the height and length of this.
0:27:37 > 0:27:42It was the highest in the world, 126ft, when it was constructed,
0:27:42 > 0:27:45and about 1,000ft long, it was also the longest.
0:27:45 > 0:27:48And it remained about the highest for 200 years.
0:27:48 > 0:27:51Just on a personal note, when you look at it, what do you make of it?
0:27:51 > 0:27:55I think it's awesome. It's awesome to walk over,
0:27:55 > 0:28:00it's very impressive, and to know that it led on to all sorts of other
0:28:00 > 0:28:02highly-engineered transport structures,
0:28:02 > 0:28:05pushing technology to the limits.
0:28:12 > 0:28:16Pontcysyllte was built at a time of great turbulence,
0:28:16 > 0:28:18of warfare and industrial revolution.
0:28:18 > 0:28:21It was an age of fire and furnace and steampower,
0:28:21 > 0:28:24of moving ever-faster, mass production.
0:28:24 > 0:28:27There was also a more sensitive spirit to this age,
0:28:27 > 0:28:31governed by an appreciation of landscape and elegance.
0:28:31 > 0:28:35This was a work of genius on both fronts.
0:28:43 > 0:28:46Subtitles by Red Bee Media Ltd
0:28:46 > 0:28:49E-mail subtitling@bbc.co.uk