Pontcysyllte Aqueduct

When we see a structure like the Pontcysyllte Aquaduct in northeast Wales, we usually assume that it is simply a bridge or a railroad trestle, but in this case, we are very wrong. While the Pontcysyllte Aqueduct is navigable, it actually carries the Llangollen Canal across the River Dee in the Vale of Llangollen. I wondered why they needed an aqueduct to carry one river over another, but the truth is that the smaller river would be swallowed up by the larger, ending any possibility of the smaller river reaching the intended destination. The 18-arched stone and cast-iron aqueduct is designed for narrowboats and was completed in 1805 after a decade of planning and construction. Measuring 12 feet in width, it stands as the longest aqueduct in Great Britain and the tallest canal aqueduct in the world.

Alongside the watercourse, there is a towpath on one side. “A towpath is a road or trail on the bank of a river, canal, or other inland waterway. The purpose of a towpath is to allow a land vehicle, beasts of burden, or a team of human pullers to tow a boat, often a barge. This mode of transport was common where sailing was impractical because of tunnels and bridges, unfavorable winds, or the narrowness of the channel.”

The Pontcysyllte Aqueduct was intended to be a central feature of the Ellesmere Canal, a proposed industrial waterway linking the River Severn at Shrewsbury with the Port of Liverpool on the River Mersey. Despite a cheaper route surveyed to the east, the chosen path traversed the Vale of Llangollen’s high ground to the west, passing through Northeast Wales’ coal-rich areas. The canal was only partially completed due to insufficient revenue generation for the entire project. Following the aqueduct’s partial completion in 1805, most significant construction stopped.

The aqueduct, designed by civil engineers Thomas Telford and William Jessop, was intended for a site near the 18th-century road crossing at Pont Cysyllte. Following the approval of the westerly high-ground route, the initial plan involved constructing a series of locks along both valley sides leading to an embankment that would carry the Ellesmere Canal over the River Dee. However, once Telford joined the project, the design shifted to an aqueduct that would provide a direct and continuous waterway across the valley. Despite widespread public doubt, Telford remained confident in his construction approach, drawing on his experience from building the Longdon-on-Tern Aqueduct, a cast-iron trough aqueduct on the Shrewsbury Canal.

The Pontcysyllte aqueduct officially opened to traffic on 26 November 1805. A plaque commemorating its inauguration reads, “The nobility and gentry, the adjacent Counties having united their efforts with the great commercial interests of this country. In creating an intercourse and union between England and North Wales by a navigable communication of the three Rivers, Severn, Dee and Mersey for the mutual benefit of agriculture and trades, caused the first stone of this aqueduct of Pontcysyllte, to be laid on the 25th day of July MDCCXCV [1795]. When Richard Myddelton of Chirk, Esq, MP one of the original patrons of the Ellesmere Canal was Lord of this manor, and in the reign of our Sovereign George the Third. When the equity of the laws, and the security of property, promoted the general welfare of the nation. While the arts and sciences flourished by his patronage and the conduct of civil life was improved by his example.”

The bridge measures 336 yards in length, 12 feet in width, and has a depth of 5 feet 3 inches. It features a cast iron trough, which is supported 126 feet above the river by iron arched ribs resting on eighteen hollow masonry piers. Each of the bridge’s 18 spans measures 53 feet across. Following the aqueduct’s completion, the canal was intended to extend to Moss Valley, Wrexham, where Telford had built a feeder reservoir lake in 1796 to supply water for the canal stretch from Trevor Basin to Chester. However, the plan to construct this section was abandoned in 1798, which lead to the neglect, and eventual abandonment, of the feeder and a navigable stretch between Ffrwd and a basin in Summerhill. Traces of the feeder channel can still be seen in Gwersyllt, and a street in the village bears the name Heol Camlas, meaning ‘canal way’ in Welsh. John Simpson of Shrewsbury, who died in 1815, oversaw the physical construction.

With the project incomplete, Trevor Basin, located just beyond the Pontcysyllte Aqueduct, became the canal’s northern terminus. By 1808, a feeder channel had been completed to transport water from the River Dee near Llangollen. To ensure a constant water supply, Telford constructed an artificial weir, known as the Horseshoe Falls, near Llantysilio to regulate the water level. The aqueduct is classified as a Grade I listed building and is a part of a UNESCO World Heritage Site.