The deepest of these channels eventually became flooded by the sea as the ice sheets receded, forming the Menai Strait.

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.

[4] 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.

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.

[5] 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.

[8] 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.

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.

[10] Over the years, the 41⁄2-ton weight limit proved problematic for the increasing freight industry and in 1938 the original wrought iron chains were replaced by a new arrangement of steel ones, without the need to close the bridge.

A statement from the Welsh Government said it was closed for essential maintenance work following safety recommendations from structural engineers.

A representation of the Menai Bridge inside a border of railings and stanchions is featured on the reverse of British one-pound coins minted in 2005.

[16] White Knight to Alice: "I heard him then, for I had just completed my design, To keep the Menai bridge from rust By boiling it in wine."