The primary purpose of a bridge is transportation and it remains so even if what is being transported is varied and the obstacle to span is either natural or man made.

At beginning of the industrial revolution, moving raw materials and completed goods was challenging, especially if the centres of industry were in remote locations or divided by natural features. Coalbrookdale in Shropshire and the surrounding area was such place. The industries developed in the 18th Century included iron making and pottery. There were deposits of coal, iron ore, limestone and clay in the vicinity, and there was also water – the great River Severn. Unfortunately, the nearest bridge was 3km away, and river crossings by boat were at the mercy of the shallows in summer and a swift current in the winter. A bridge was needed to cross the gorge, a single span and high enough to allow ships to pass beneath. The architect chosen, Thomas Farnon-Pritchard suggested to his friend, ironmaster, John Wilkinson, in 1773 to use cast iron. It had never been used before in bridge building.

Wilkinson was a prolific inventor especially of anything involving iron. His machine tools help bore cylinders for James Watt’s steam engines. And crucial to the success of Ironbridge’s legacy, he was the driving force for pushing the need for a bridge through parliament. He particularly wanted to help connect his town of Broseley with the other side of the River Severn.

Pritchard himself, although a professional architect, was more of an interior designer who specialised in chimney pieces and funerary monuments with Rococo or Gothic styles and his influences can definitely be seen in the arch. The Royal Act to build a bridge received consent in 1776, and Coalbrookdale’s own ironmaster Abraham Darby III was commissioned to cast and build the bridge having put in a bid. Wilkinson sold his shares to Darby in 1777.

The ironworks had to produce 384 tons of iron, requiring the furnaces to work solidly for three months, and the iron was used to make over 1,700 individual elements. Pritchard died before the bridge was completed in 1781 and it was the only bridge he ever designed. The finished bridge became famed for the intricate, almost decorative styling he envisaged. The Ironbridge, which subsequently became the name of the surrounding village, influenced many subsequent bridge builders, and is the iconic representation of the Industrial Revolution. This legacy was further helped by the artists who witnessed and captured the transformation of the area in their paintings and engravings. Darby encouraged the promotion of the bridge to advertise his skills as an iron caster. The symmetrical design suits the landscape perfectly, especially when viewed from upstream as the reflection completes the arch’s circle.

The visual impact of a bridge is now very much a feature of a modern architecture. While transportation of goods and vehicles remains key, there has been a rebirth in pedestrian and cycle crossings in the 21st century, as people seek to address environmental issues.

These new bridges are as novel as the Ironbridge, but they remain anchored in the physics of fundamental engineering. The Infinity Bridge in Stockton on Tees is based on the tied arch or Bowstring bridge. Its uniqueness being a pair of different sized steel tied arches with a suspended concrete deck. The asymmetrical nature is enhanced by illumination with LED lighting built into the handrails. The reason for this is to do with the bridge’s name. At night, when the river is calm, the twin arches cast a reflection, and together, bridge and reflection form the infinity symbol.

Over two centuries apart, Ironbridge and Infinity perform their transport functions well (although Ironbridge no longer takes vehicles), but what remains most notable and enduring is their aesthetic appeal, whether symmetrical or asymmetrical.