Pontcysyllte Aqueduct
Walk across Pontcysyllte and you're 126 feet above the River Dee on a cast-iron trough of water, with nothing but a thin rail between you and the drop.
Published
Quick Facts
- Location
- Near Froncysyllte and Trevor, east of Llangollen, Wrexham county, north-east Wales
- Opened
- 1805, after about ten years of construction
- Height
- About 126 feet (38 metres) above the River Dee
- Length
- About 1,007 feet (307 metres)
- Structure
- 18 stone piers carrying a cast-iron trough, with 19 arches
- Engineers
- Thomas Telford and William Jessop
- Carries
- The Llangollen Canal
- Recognition
- UNESCO World Heritage Site since 2009; Grade I listed
A canal in the sky
Most famous bridges carry people. Pontcysyllte carries a river of its own. Boats glide along a narrow iron trough, filled with water, high above the valley of the River Dee. It is the longest aqueduct in Britain and the highest canal aqueduct in the world. Stand underneath it and you'll struggle to believe that something so slender can hold up a canal full of water and a string of narrowboats. The name is Welsh and means roughly 'the bridge that connects', from the nearby Cysyllte township. Locals often shorten it to simply 'Pontcysyllte', and many English visitors give up and call it 'the aqueduct in the sky'.
Why build it at all?
The aqueduct was part of the plan for the Ellesmere Canal, which was meant to link the Mersey, the Dee and the Severn and carry coal, lime, iron and slate through the borderlands. The Dee valley stood squarely in the way. The obvious answer was a flight of locks down one side and back up the other, but that would have demanded a huge supply of water and a great deal of time. Engineers William Jessop and Thomas Telford chose to go straight over the top instead. The canal never became the grand through-route its backers dreamed of. Its life was mainly local, and water from the Dee was later fed into it at Llantysilio, which is why the canal still runs today as the Llangollen Canal.
Telford's clever tricks
Building something this tall in the 1790s took invention. The piers are hollow in their upper sections, saving weight without sacrificing strength. The stone was laid with mortar said to contain lime, water and ox blood, a recipe used by builders of the time. The trough itself is made of cast-iron plates bolted together, with joints sealed using Welsh flannel dipped in boiling sugar and then lead. Later repairs have of course used modern materials, but the structure remains essentially as completed. It cost around £47,000, and the work was finished in 1805. Telford went on to build the Menai Suspension Bridge and the Caledonian Canal, but Pontcysyllte is often counted among his boldest achievements.
The side with no wall
Here is the detail that makes visitors gasp. On one side, the towpath has a handrail and a path for walkers. On the other side, there is nothing: the iron trough simply rises a few inches above the waterline, then the air begins. Boaters steering across have a clear view straight down to the Dee, 126 feet below. Some love it, and others admit to staring firmly at the far end of the bridge. There is a reason for the open design. The aqueduct was made as light as possible, and the unobstructed side kept the weight of the whole structure down.
Walking it, paddling it, or staring up at it
You can cross on foot, by narrowboat or by canoe, and each gives a very different sense of the place. Walkers on the towpath get a close view of the valley, while boaters glide through a long moment of weightless calm. For the best look at the whole thing, head down into the valley and view it from below, where the line of arches stretches across the trees. The nearby Trevor Basin makes a natural starting point, and it is only a short walk from the aqueduct. Look out for the stone piers' gentle taper and the line of the trough along the top, and spot the narrowboats crossing like toys against the sky.
From working canal to World Heritage Site
Commercial traffic faded in the twentieth century, and the canal might have been abandoned like many others. Instead, a growing leisure boating scene kept it alive, and the aqueduct is now a Grade I listed structure. In 2009 UNESCO inscribed the Pontcysyllte Aqueduct and Canal as a World Heritage Site, recognising it as a masterpiece of the Industrial Revolution and a pioneering work of civil engineering. The site includes about eleven miles of canal, taking in Chirk Aqueduct and Chirk Tunnel, and running through to Horseshoe Falls near Llangollen. More than two centuries on, it still does the job it was built for: carrying water, and boats, across a valley.
Notable people
- Thomas Telford
- William Jessop