The Menai Suspension Bridge (Welsh: Pont y Borth or Pont Grog y Borth) is a suspension bridge spanning the Menai Strait between the island of Anglesey and the mainland of Wales. Designed by Thomas Telford and completed in 1826, it was one of the world's first major suspension bridges, and second such bridge designed to carry vehicular traffic, after the Union Chain Bridge (1820) across the River Tweed. The bridge still carries road traffic and is a Grade I listed structure.
Background The Menai Strait was created by glacial erosion along a line of weakness associated with the Menai Strait fault system. During a series of Pleistocene glaciations (that lasted from about 2,580,000 to 11,700 years ago), a succession of ice-sheets moved from northeast to southwest across Anglesey and neighbouring Gwynedd, scouring the underlying rock and creating a series of linear bedrock hollows. The deepest of these channels eventually became flooded by the sea as the ice sheets receded, forming the Menai Strait. As Anglesey has been an island throughout recorded human history, the only way to reach it was by crossing the strait. However, this has always been a dangerous endeavour because there are four strong tidal flows each day generated by the twice daily tides. These flow in both directions through the strait, creating strong currents and whirlpools. Despite the dangers, ferries operated all along the Menai Strait, carrying passengers and goods between the island and the mainland. In 1785, a boat carrying 55 people ran aground at the southern end of the Menai Strait in a strong gale and began to sink. The stricken vessel sank before a rescue boat from Caernarfon could reach it, and only one person survived. Additionally, the main source of income on Anglesey was from the sale of cattle, and to move them to the markets of the mainland, including London, they had to be driven into the water and encouraged to swim across the Strait. This often resulted in the loss of valuable animals. In 1800, Ireland joined Great Britain in the Act of Union. This led rapidly to an increase in people travelling between London and Holyhead en route to Dublin. In 1815, the British Parliament passed an act of Parliament, the Holyhead Roads Act 1815 (55 Geo. 3. c. 152), to build the Holyhead Road with responsibility for the project given to civil engineer Thomas Telford. Despite some difficult geographical obstacles to overcome (e.g. Snowdonia and the Menai Strait), the route was chosen because Holyhead was the principal port for ferries to Dublin as it was the closest point to Ireland. After Telford had completed a survey of the route from London to Holyhead, he proposed that the best option was to build a bridge over the Menai Strait from a point near Bangor on the mainland to the village of Porthaethwy (now commonly known as Menai Bridge) on Anglesey. The site for the bridge was chosen because it had tall banks that would be high enough to allow sailing ships to pass underneath. Telford proposed that a suspension bridge would be the best option because it would have a span wide enough to cross the fast flowing waters of the Strait at this point. His recommendation was accepted by Parliament, which authorised the bridge in the Roads Between London and Holyhead Act 1819 (59 Geo. 3. c. 48).
Construction
Construction of the bridge, to Telford's design, began in 1819 with the towers on either side of the strait. These were constructed from Penmon limestone and were hollow with internal cross-walls. Then came the sixteen huge chain cables to support the 176-metre (577 ft) span, each consisting of five parallel bars of wrought iron links, for a total of 80 iron bars and 935 links per cable. The chains were carried over the piers on cast iron saddles with rollers, allowing for movement caused by temperature changes. Each chain measured 522.3 metres (1,714 ft) and weighed 121 long tons (123 t; 136 short tons). Their suspending power was calculated at 2,016 long tons (2,048 t; 2,258 short tons). To avoid rusting between manufacture and use, the iron was soaked in linseed oil and later painted. On both sides of the strait the chains were conveyed through three tunnels into a chamber cut into the rock, where they were held in place by 9 feet (2.7 m) bolts resting in cast iron sockets. William Hazledine was contracted to supply the necessary wrought and cast iron, and each chain had four adjusting links to compensate for differences in length caused by imperfections during the production of the large number of separate links. Workmen assembled the majority of the chains link by link on-site. This was carried out on platforms near the tunnel mouths until the chains, supported by scaffolding, reached the tops of the piers. A cradle capable of carrying two workers was then suspended from each tower and links were lifted up and attached by the men in the cradles until the chains reached water level. The final central portion of each chain was floated across on a 400 feet (120 m) raft and lifted via a system of pulleys by 150 men. The bridge was opened to much fanfare on 30 January 1826. It reduced the 36-hour journey time from London to Holyhead by 9 hours.
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