I defy anyone not to be moved by the sheer engineering genius, foresight, and confidence of Isambard Kingdom Brunel's design for this bridge, which carries the Great Western Railway main line over the River Thames. The bridge actually has two of these arches, which at the time of their building in 1838 were the widest and flattest in the world. Each span is 128 feet (about 39 metres), with a rise of only 24 feet (about 7 metres). This arch is known as the Sounding Arch, because of its spectacular echo. There is a circular stone plaque giving these details on the bridge abutment just visible on the right side of the photo.
It has been claimed that the board of the Great Western Railway did not believe that the arches would stay up under the weight of the trains and ordered Brunel to leave the wooden formwork used to construct the arches in place. However, Brunel simply lowered the formwork slightly so that it had no structural effect, but appeared to be in place. Later, when the formwork was washed away in floods, but the bridge remained, the strength of the arches was accepted.
As built, the bridge carried two lines of Brunel's broad gauge track. Subsequently the bridge was widened, and now carries the four lines of standard gauge track that make up the Great Western Main Line out of London Paddington Station.
The bridge also features in J M W Turner's 1844 painting entitled Rain, Steam and Speed - The Great Western Railway, now in the National Gallery, London Link