World Heritage Sites in Wales

This story describes the background to the designation of UNESCO World Heritage Sites (WHS) and summarises the main details of the three sites that are within Wales, further information can be found at

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Pontcysyllte aqueduct

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Quarrymen splitting a large block of slate in...

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Composite WHS Picture

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Blaenavon Regenerated Streets


The World Heritage Convention of 1972 recognizes that heritage can be in both cultural and natural forms. The convention has now been ratified by 187 state parties and there are currently 938 sites on the World Heritage List that are spread over 153 states.

Sites are nominated by the government of the country in which they are located and they must meet one or more of the ten criteria that are set by the UNESCO World Heritage Committee. The criteria are used to assess the Outstanding Universal Value of a site and identify whether it may be regarded as having made a unique contribution to a shared global heritage. Once a site has been inscribed on the World Heritage list, the entire world then shares the responsibility for its continued preservation and conservation.

Across the globe, a total of 725 World Heritage Sites are recognised for their cultural value, while 183 relate to natural sites and 28 sites are mixed. In the United Kingdom there are a total of 28 sites and of these 3 are within Wales. These are; Pontcysyllte Aqueduct and Canal, Blaenavon Industrial Landscape and the Castles and Town Walls of King Edward in Gwynedd. A further World Heritage Site is proposed in the Slate Quarries of North Wales.

The most recent of the World Heritage Sites in Wales to have been recognized by UNESCO, is the Pontcysyllte Aqueduct and Canal that was designated in 2009. 

Sources: a PowerPoint Presentation by Dr Peter Wakelin at the RCAHMW Open Day 23 July 2011.

Pontcysyllte Aqueduct and Canal

Pontcysyllte Aqueduct has been described as one of the world’s greatest engineering achievements. It was built between 1795 and 1805, by William Jessop and Thomas Telford, to carry the Ellesmere Canal across the Dee valley. This provided a link between the coal mines of Denbighshire, through the national canal system, to the heartlands of the Industrial Revolution. At a height of 39 metres and a length of 307 metres the aqueduct was the tallest and longest navigable aqueduct in the world, and remained so for the next 200 years.

A pioneering technique in the use of cast iron had enabled its construction and the aqueduct is considered to be an excellent example of the new industrial age. Telford and Jessop also devised a new method of stone construction to allow the piers to reach a sufficient height. The piers were built with tapered, hollow top sections, and this reduced the volume and weight of the stonework.

The arches and trough of the aqueduct were made of cast iron, and were produced at a specially commissioned forge at nearby Plas Kynaston. Each of the eighteen spans was supported by four arch ribs, cast in three sections and bolted together with connecting plates to maintain flexibility. The trough, holding the canal, was designed to sit on top of the ribs, with lateral movement being prevented by brackets and lugs, weighted down by the volume of water.

The aqueduct was constructed with stone from a quarry on the northern side of the river. Firstly the stone piers were built in stages starting with the lower sections of the river piers. Then moving south to north across the valley, the piers were raised between six and eight metres in height at a time. Five timber gangways were constructed to transport materials and provide working platforms. From evidence in the stone work of each pier, it is understood that each gangway rested on two timber beams, which were supported by the stonework of the piers, with diagonal braces held in cast iron shoes and secured to the stonework. 

 The towpath was designed to enable circulation of water underneath it that would prevent an overflow.  In 1831 the original wooden towpath was replaced with a cantilevered design that is still in existence.

Pontcysyllte Aqueduct and Canal meet several of the World Heritage Convention criteria. Firstly they represent ‘a masterpiece of human creative genius’, secondly they ‘exhibit an important interchange of human values… on developments in architecture or technology…’and the site also meets the criterion (number iv on the UNESCO list) to ‘be an outstanding example of a type of building or architectural or technological ensemble… which illustrates a significant stage in human history’.

The World Heritage Site represents an outstanding example of transport in the first Industrial Revolution that linked British coalfields in the 1790s and 1800s.

Link to an animation showing the construction of Pontcysyllte:


Wakelin,P  & Griffiths, R.A (2008)’Hidden Histories, Discovering the Heritage of Wales’ RCAHMW p.192. Aqueduct

Blaenavon Industrial Landscape

In the year 2000, the Blaenavon Industrial Landscape was inscribed by the World Heritage Committee. The World Heritage Site is focussed on the Blaenavon Ironworks and its surroundings, with a full extent of 3,290 hectares, nearly half of which is located within the Brecon Beacons National Park. This area encompasses; The Big Pit National Mining Museum, Blaenavon Town, The Blaenavon World Heritage Centre, The Canal, Keeper’s Pond and the Pontypool and Blaenavon Railway.

Blaenavon Ironworks were established on Lord Abergavenny’s Hill by three industrialists, Thomas Hill, Thomas Hopkins and Benjamin Pratt, in 1789. They established the most modern ironworks in the world, which is now well preserved and maintained by Cadw.

The Big Pit mine included a number of earlier mines as well as the main shaft that was sunk in 1860 and deepened in 1880. The mines in the area had previously been used for the collection of ironstone, for the iron works. Through the nineteenth century there was a growing demand for coal and this gradually replaced iron and steel as the focus of industry. Following the decline of the coal industry towards the end of the twentieth century, the Big Pit was converted a museum, which opened in 1983 and is now the National Coal Museum of Wales.

Blaenavon Town began to develop along with the ironworks in the 1780s. At first housing was provided for the industrial workers and this included Stack Square that was used in the BBC’s Coal House series. The iron masters mansion, known as Ty Mawr, was built between 1798 and 1800 and St Peters Church was built in 1804. The town centre developed during the middle of the nineteenth century, largely due to the influence of a local businessman, John Griffith William, and the emerging Urban District and Ecclesiastical Parish of Blaenavon. The town centre was designated as a Conservation Area in 1984.

The focus for intellectual and physical access to the Blaenavon Industrial Landscape is provided through the World Heritage Centre and Tourist Information Centre that is located in the building of St Peters School. The school was built in 1816 by Sarah Hopkins, in memory of her brother Samuel, and it was the first school in Wales to be purpose built by an individual proprietor for children of the workforce.

Further remains of the industrial era are now used for leisure, these include; The Canal, that provided an export route for iron and coal production from 1816 to 1860, The Keeper’s Pond that was created in 1817 to supply water to the Garnddyrys Forge, and a section of the Pontypool and Blaenavon Railway.

The Industrial Landscape is considered by UNESCO to be “an exceptional illustration in material form of the social and economic structure of nineteenth century industry” and “an outstanding and remarkably complete example of nineteenth century industrial landscape”.

Sources: Blaenavon World Heritage Site Area (and associated sites)

Castles and Town Walls of King Edward in Gwynedd

The castles and fortified towns of Gwynedd are considered to be the finest examples of late thirteenth and early fourteenth century military architecture in Europe. They were the first of the World Heritage Sites within Wales to be designated by UNESCO in 1986.

Their construction began in 1283 and continued until the early 1330s. They demonstrate typical forms of medieval architecture including; barbicans, drawbridges, fortified gates, chicanes, redoubts, dungeons, towers and curtain walls.

Beaumaris Castle, on the island of Anglesey, Caernarvon and Conwy castles and their town walls, and Harlech Castle, north of Cardigan Bay, were all built by the king's chief architect, James de St George, who was also the constable of Harlech from 1290 to 1293.The series of castles were established to secure North Wales following the death of Llywelyn ap Gruffudd in 1282 although the construction was sometimeshindered by the Welsh uprisings of Madog ap Llywelyn in 1294.

The castles of Beaumaris and Harlech have a very similar design that consists of an inner wall surrounded by an octagonal wall and flanked by towers. The double-wall structure is characteristic of late thirteenth century military architecture. Beaumaris Castle was never finished although Harlech was largely completed by 1289. During the Welsh rebellion, Harlech Castle became occupied by Owain Glyndwr’s court and family until it was retaken by the English in 1409.

The Caernarvon and Conwy castles and fortified towns demonstrated King Edward I's military and settlement policy as they would have been populated by English settlers. Caernarvon Castle consists of seven great polygonal towers, two turrets and two great twin towered gates, joined by curtain walls. The investiture of Prince Charles, the current Prince of Wales, took place at the castle in 1969.

Conwy Castle was finished in 1287 and it has eight towers. The castle’s medieval chambers are largely unaltered and remain in good condition. In 1401 the castle was captured by supporters of Owain Glyndwr.  In the nineteenth century Thomas Telford constructed the Conwy Suspension Bridge with battlemented towers that were designed to reflect the architecture of the castle.

Community Benefits of World Heritage Site Status

World Heritage Sites tend to attract visitors and this may bring social and economic benefits to an area.  These effects have been particularly noticeable in the Blaenavon Industrial Landscape where the town of Blaenavon had been in decline throughout the twentieth century.

After coal replaced iron and steel as the dominant industry during the nineteenth century, there was a decline during the Great Depression in the 1920s and 1930s. Following the Second World War the town remained reliant on the coal industry, which had a rapid decline in the 1980s. Fortunately, the heritage potential of the area was recognized in the process of regeneration.

 In 1997 the Blaenavon Partnership was formed and they aimed to achieve UNESCO World Heritage status for the town. After the area was inscribed as a World Heritage Site in November 2000, this enabled the community to seek funding from other public bodies.

Money was invested into improved historical interpretation, the Blaenavon Cordell and Community Heritage Museum was opened in 2001 and the Blaenavon World Heritage Centre was opened in 2008. Outdoor recreation was promoted through the Blaenavon Community Woodland, the Cycle Route, Garn Lakes and the publication of a series of walking leaflets. The Iron Mountain Trail was launched in 2005.

The status of World Heritage Site has provided a catalyst for the restoration and re-use of derelict buildings. The old Blaenavon Council Offices were converted into the new library and St Peters School is used as the World Heritage Centre. Property improvement grants allowed private homes to be restored with historic features. In the main commercial street, Bow Street, old photographs were examined and the shops that were previously boarded up with plywood were regenerated as a shopping centre with Victorian frontages.

Cultural activities are encouraged and events including the Spring Festival, World Heritage Day and the Garn Lakes Country Fayre take place in the town. Since receiving World Heritage status in 2000 the town has experienced urban and environmental regeneration that has brought great improvement to the area during the twenty-first century.


A further WHS for Wales

A further World Heritage Site in Wales is proposed in the ‘UK Tentative List of Potential Sites for World Heritage Nomination’, and this is ‘The Slate Industry of North Wales’.

The proposal relates to several areas that provide authentic examples of the slate quarrying industry and its associated transport, infrastructure and communities. The component sites include; Ogwen-Cegin slate-quarrying landscape, Penrhyn Castle, the Welsh Slate Museum, the slate-quarrying landscape of Nantlle/Moel Tryfan, the Gorsedda quarry, the Ffestinog slate landscape and railway, and the University building. These sites still have their original fabric from a significant period of 1856 to 1914.

The slate industry provided roofing products throughout the world during the nineteenth century and the industry had a significant impact on the surrounding mountainous landscape. The communities that worked in the slate quarries were Welsh speaking and the proposed site is considered to be an exceptional example of how a minority cultural and linguistic tradition adapted to the nineteenth century.

The site is also associated with achievements in social justice through the workers chapel and their support for the University of Bangor. The inscription as a World Heritage Site would, “support conservation of the area's unique cultural, historic and industrial assets”, and, “assist regeneration in the associated towns and villages and aid conservation and protection of the industry's features through raised awareness and increased community pride”.

Source: UK Tentative List of Potential Sites for World Heritage Nomination: Application for SLATE INDUSTRY OF NORTH WALES:

Claire Parry, RCAHMW, 29 September 2011

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