The Menai Suspension Bridge, Pont Grog y Borth, spans the Menai Strait between Anglesey and mainland Wales. It is the first modern suspension bridge and was designed by Thomas Telford and completed in 1826.
Before 1826, Anglesey had no fixed connection to mainland Wales. Most crossings were done by ferry but it was possible to to cross on foot. Cattle was driven into the water to swim across the strait then driven to the London markets. When Holyhead became a major terminal to Dublin crossing the Menai Strait had to be improved.
Thomas Telford was given the challenge of building a bridge across the Menai Strait. He had to design a bridge that would allow Royal Navy sailing ships 100 feet tall to pass underneath at high tide. He chose a point near Bangor and the village of Porthaethwy on Anglesey.
Construction began in 1819 with the two towers on either side of the strait using Penmon limestone. These towers are hollow. Sixteen chain cables, each made of 935 iron bars to support the 176m deck, were strung across the towers. These were soaked in linseed oil then painted. The bridge was opened in 1826 and cut the travelling time from London to Holyhead by nine hours.
In 1839 the bridge was damaged by high winds, in 1893 the wooden deck was replaced by a steel deck. In 1938 the wrought iron chains were replaced with steel cables without closing the bridge. In 1999 the bridge was closed to resurface the road and strengthen the structure.