22 CONTEXT 176 : JUNE 2023 to terminate at Horseshoe Falls. This unique and distinctively curved cast-iron and masonry weir, 140 metres long, impounds water from the River Dee to supply the Ellesmere Canal and to help supply drinking water to southern Cheshire. Somewhat overlooked among the other, more elaborate, structures within the world heritage site is a further cast-iron innovation found within three relatively modest stone bridges that traverse the canal. These unusual composite bridges employ curved cast-iron beams supporting shallow masonry arches. These allowed the necessary headroom beneath the span while reducing the required gradient of the approach road to either side. Pontcysyllte Aqueduct and Canal is by no means the only canal-based world heritage site in the world. Canals feature heavily in some world heritage site cities such as Strasbourg, Venice, Bruges and Amsterdam, and there are others inscribed specifically because of the historic importance of man-made water systems. The Grand Canal in China has its origin as far back as the fifth century BC, its extensive network of communication waterways being recognised as the earliest man-made waterway network in the world. The 360-kilometrelong Canal du Midi in south-western France also pre-dates the Llangollen Canal by a century and is recognised as having influenced the pioneers of British canal construction. The 202-kilometre-long Rideau Canal in Canada, completed in 1832, was a strategic military canal. It utilised technology already tried and tested in the UK and Europe, such as on the Ellesmere Canal, assisting the British to defend the colony of Canada against the USA. However, it is the monumental scale of the engineering, and the innovative use of materials, most notably cast and wrought iron, that make Pontcysyllte Aqueduct and Canal World Heritage Site universally outstanding. At the time of its completion, the length of canal was described as being, ‘composed of works more difficult of execution than can perhaps be found anywhere within an equal distance of canal navigation’, in part due to the desire of its engineers to overcome the difficult terrain of two major river valleys, and the ridge of ground between them, without wishing to follow the topography or create time-consuming and resource-hungry lock flights. The inscribed length of the Llangollen Canal is multi-designated, and is both a Cadw and Historic England scheduled monument. It also bisects the Offa’s Dyke scheduled monument west of Pentre. In addition, there are 25 listed structures (bridges, tunnels, aqueducts, culverts and weirs) directly associated with the navigable canal channel itself, and a number of buildings and structures relating to the historic operation of the canal. The principal structure within the world heritage site, Pontcysyllte Aqueduct, is Grade I listed, while Chirk Aqueduct and Chirk Tunnel are both listed at Grade II*. There are three conservation areas along the length of the inscribed section of canal, two relating to the settlements of Chirk and Llangollen, the other relating to the area around the settlement of Froncysyllte, the Pontcysyllte Aqueduct and Trevor Basin. As well as these heritage designations, the world heritage site runs through the Clwydian Range and Dee Valley Area of Outstanding Natural Beauty. The Horseshoe Falls weir, designed by Thomas Telford, helps create a pool of water that can enter the Llangollen Canal. (Photo: Chris Davies)
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