Full Reports of World Heritage Site

SummaryDescription of World Heritage Site

Reference Number
Pontcysyllte Aqueduct and Canal  
Date of Designation


Unitary Authority
Llangollen Rural  

Broad Class
Water Supply and Drainage  
Site Type
Post Medieval/Modern  


Description of World Heritage Site
Brief synthesis The Pontcysyllte Canal is a remarkable example of the construction of a human-engineered waterway in a difficult geographical environment, at the end of the 18th century and the start of the 19th century. It required extensive and boldly conceived civil engineering works. The Pontcysyllte Aqueduct is a pioneering masterpiece of engineering and monumental architecture by the famous civil engineer Thomas Telford. It was constructed using metal arches supported by tall, slender masonry piers. The Pontcysyllte Aqueduct and Canal are early and outstanding examples of the innovations brought about by the Industrial Revolution in Britain, where they made decisive development in transport capacities possible. They bear witness to very substantial international interchanges and influences in the fields of inland waterways, civil engineering, land-use planning, and the application of iron in structural design. Criterion (i): The Pontcysyllte Aqueduct is a highly innovative monumental civil engineering structure, made using metal arches supported by high, slender masonry piers. It is the first great masterpiece of the civil engineer Thomas Telford and formed the basis of his outstanding international reputation. It bears witness to the production capacities of the British iron-making industry, which were unique at that time. Criterion (ii): The intensive construction of canals in Great Britain, from the second half of the 18th century onwards, and that of the Pontcysyllte Canal in particular in a difficult region, bear witness to considerable technical interchanges and decisive progress in the design and construction of artificial waterways. Criterion (iv): The Pontcysyllte Canal and its civil engineering structures bear witness to a crucial stage in the development of heavy cargo transport in order to further the Industrial Revolution. They are outstanding representatives of its new technical and monumental possibilities. Integrity and authenticity The integrity of the waterway has been maintained in hydraulic and civil-engineering structures that have remained in their original form. However, the historic embankments, made of rubble, have raised significant problems of stability and waterproofing, particularly in the second half of the 20th century. The repairs have involved the use of technical solutions that are different from the simple initial backfills, both for structural resistance and waterproofing: concrete, steel pilings, geotextiles, etc. From the point of view of integrity, these works have made it possible to maintain the hydraulic operation of the waterway and to conserve its overall morphological characteristics. The integrity of the landscapes and the buffer zone of the property contributes to the expression of the value of the property. The property has all the elements of integrity necessary for the expression of its value, as a major historic canal of the Industrial Revolution. The few structural changes that have been made to the two large aqueducts have remained secondary, contributing to maintaining the property in use. Changes in materials have remained restricted over the history of the property. During the 20th century repairs to masonry did not always use the original types of mortar or stone. The buildings associated with the canal and its immediate environment usually achieve a good degree of authenticity HISTORICAL SUMMARY In order to link Chester and the Mersey estuary to the Severn and the Midlands canal network, the Ellesmere Canal was conceived in the early 1790s. It was undertaken by a private company under the technical supervision of the engineer William Jessop (1745-1814). The construction of three branches was started from the central point of Ellesmere. The need for water and the rich reserves of coal and limestone in the Dee and Ceiriog valleys, in the foothills of the Welsh mountains, led to the extension of the project in this direction by a fourth section. The works began in 1795. However, linking the northern side of the Dee to the Ellesmere canals, crossing the Rivers Ceiriog and Dee, which have very pronounced valleys, presented two major obstacles. From 1793 onwards, Jessop worked in collaboration with Thomas Telford (1757-1834) for this branch of the canal. Telford was an outstanding engineer and architect who had a remarkable ability for finding new technical solutions to building and civil-engineering problems. He was already well known when he was engaged and had just undertaken the construction of several cast-iron bridges, such as the Longdon aqueduct to cross the Severn. He also proposed a cast-iron bridge to cross the Thames. In the same region he was also employed to build the road from London to Dublin. The aqueduct over the Ceiriog at Chirk was the first structure to be planned, in 1795, by Jessop and Telford. After considerable discussion a stone structure was preferred. Shortly afterwards, when the crossing of the Dee came up for consideration, the conditions were different. The valley was wider and deeper, and a conventional aqueduct would therefore have been be very costly; furthermore, cast-iron bridges were beginning to prove their qualities. The cast-iron bridge solution proposed by Telford was chosen and construction work began under his supervision. The canal up to Trevor was opened on 26 November 1805. The part which extends the canal to Horseshoe Falls was completed in 1808. As soon as it had been built the Pontcysyllte aqueduct became famous for its highly innovative technical and architectural boldness. When completed it was recognised as an outstanding success, eliciting praise from engineers and inspiring Romantic artists. After the end of the Napoleonic wars several foreign engineers and scholars came to visit the aqueduct. The Pontcysyllte aqueduct made Thomas Telford famous. He was recognised in his lifetime as the greatest builder of iron bridges and canals of his time. He became the first president of the Institution of Civil Engineers in London in 1825. Telford and his Pontcysyllte aqueduct had an important influence in the international development of canals at the beginning of the 19th century in Great Britain, Europe and North America. Telford participated in the construction of other very well known canals, such as the Caledonian Canal in Scotland and the Göta Canal in Sweden. The economic influence of the canal for the region was considerable during the first half of the 19th century, enabling the rapid development of coal extraction, metal working, limestone quarries, and the production of lime. The slate quarries of the Welsh mountains and agriculture also benefited from the canal. By 1815 the substantial investments it had required had been repaid and the canal became a highly profitable business. Its direct link with a vast network of canals to the Mersey, through the Midlands, and as far as London, greatly encouraged the use of the canal. The situation here was different from that in other regions because the railway was not a direct competitor to the canal but was instead basically complementary, through small private lines that led up to the canal. However, the activity of heavy cargo transport went into a steep decline at the end of the 19th century as the growth of local heavy industry contracted. Economic traffic dropped to a negligible level even before World War I. As the landscape environment remained rural and the valleys were pleasant - despite the presence of industry, which never profoundly changed them - canal tourism began as early as 1884. Throughout the first third of the 20th century canal tourism was both regular and organised, in the form of small cruises and stays in countryside locations. However, the crisis of the 1930s, followed by the war, dealt the canal a fatal blow. In 1944 the Ellesmere Canal was decommissioned by an Act of Parliament, but its western branch was conserved, under the name of the Llangollen Canal, because of its role in the regional water supply. It was, however, in poor condition and no longer navigable, and the aqueduct therefore no longer carried any boats. Efforts to encourage pleasure cruising and the preservation of the industrial heritage, led by enthusiastic historians and writers, generated a renewal of interest in the early 1950s. This led to a real lift-off for tourism in the 1960s in Great Britain, which contributed to the restoration of the canal and its maintenance. Since 1954 it has been managed and maintained in a navigable condition by British Waterways. This canal is one of the most popular and frequented in the United Kingdom. During the 19th century the canal and its engineering structures were regularly maintained. No structural changes were made; wharves and buildings were, however, built on its banks to meet transport needs. The waterproofing of the Chirk Aqueduct was restored in 1866-68 with the addition of cast-iron plate sections at the ends. Some changes of individual metal parts have been carried out on the Pontcysyllte Aqueduct; its towpath was relaid with cast-iron plates in 1879. Because of the relatively early decline of its industrial activity at the end of the 19th century, it has not undergone any major transformation. It thus well reflects the Industrial Revolution period and its waterway transport. Fill embankment collapses occurred in 1945, 1960, 1982 and 1985, requiring substantial repair work at certain points on the canal. This was an important point to ensure the maintaining of the integrity of the waterway. The Pontcysyllte Aqueduct was completely renovated in 2003-2004 to mark its bicentenary, with every effort being made to respect its technical heritage. The work consisted of removing corrosion on the cast iron, changing defective metal parts by others of the same form and of similar materials, repairing the pier masonry, and completely restoring the towpath and its railings, which were in a poor state of repair. The Pontcysyllte Canal and Aqueduct have inspired canal preservation policy in Great Britain and have made a strong contribution to raising awareness of the heritage left behind by the industrial period.  

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