It would be very remiss of me if I didn’t dedicate today’s letter to Thomas Telford (1757-1834), a Scottish engineer, and perhaps Britain’s greatest civil engineer whose nickname is the “Colossus of Roads”. His architectural and construction plans include canals, harbours and bridges of which there are 120 in Scotland.
His origins are very humble. He was born to a shepherd on the Scottish Borders, but was raised by his widowed mother after his father died when he was still a baby. Telford spent much of his early childhood shepherding while attending school. At fourteen he became a stonemason’s apprentice and built his first road on the estate of a local duke.
By twenty-five he was in London. There he acquired a wealthy patron William Pulteney MP – the same family as the Pulteney’s in Bath. Telford taught himself civil engineering from basic construction to the best materials. He was very keen on the materials being right for the job.
Pulteney gave him a project of renovating the derelict Shrewsbury Castle into a home, so Telford obligingly turn the Norman motte and bailey into a house, complete with a folly tower for the MP’s wife. Telford’s reputation was further enhanced when he surveyed a church with a leaky roof. He warned the parishioners that the church was about to collapse. It duly fell down three days later. Pulteney then ensured Telford was given the job of surveyor of works in Shropshire. The county surveyor is responsible for civil architecture. In this role he planned, amongst other things, bridges – forty in Shropshire.
One post alone can’t do justice to Thomas Telford, so I’m going to tell you about three bridges, starting with Craigellachie Bridge in Moray, Scotland.
The bridge has a single span of 46 metres over the River Spey and is made of cast iron. The ironwork was made in Wales, which was transported on the Ellesmere Canal (built by Telford) along the Pontcysyllte aqueduct (built by Telford) then by sea to Speymouth. The iron has a high tensile strength, something probably specified by Telford. He liked to test materials, and was one of the first engineers to do this thoroughly before building. He considered the iron used in Ironbridge to be poorly cast. Craigellachie was part of major project to transform the transport system of the Highlands; he added or improved 920 miles of roads, a sixty mile canal, harbours and thirty-two churches. The plan took twenty years to execute.
The next bridge is Conwy Suspension Bridge in Conwy, North Wales. It is one of the earliest road suspension bridges and was completed in 1826. The bridge looks spectacular next to the world heritage site of Conwy Castle and he designed it to match the castle, including castellated towers and machicolations (murder holes for pouring oil). The bridge is now managed by the National Trust and is not open to traffic. Unfortunately two bridges were built on either side of it rather ruining the vista.
But the grandest and most famous of Telford’s bridges is Menai Suspension Bridge, which was also finished in 1826. The bridge connects the Island of Anglesey (including the important port of Holyhead) to mainland Wales. The site of the bridge was chosen for its high banks, allowing ships to pass beneath. Sixteen wrought iron chain cables were needed to support the 176 metre span. To prevent rusting the iron was soaked in linseed oil after manufacturing. Each chain had four adjusting links to allow for different lengths caused by production imperfections. Telford really thought ahead! The bridge reduced the journey time from London to Holyhead by nine hours. At the time it was the biggest suspension in the world. It wasn’t until 1936 that the iron chain cables were replaced with steel.
Telford died in 1834 and is buried in Westminster Abbey. The civil engineer’s name can be found on roads, colleges, bridges and a whole ‘new’ town Telford is named after him. It’s appropriate that the town is in Shropshire where Telford’s career took off, but his greatest legacy will always be in Scotland.