The Causey Arch is a bridge near Stanley in County Durham, northern England. It is the oldest surviving single-arch railway bridge in the world, and a key element of the industrial heritage of England.
It was built in 1725–26 by stonemason Ralph Wood, funded by a conglomeration of coal-owners known as the “Grand Allies” (founded by Colonel Liddell and the Hon. Charles Montague) at a cost of £12,000. Two tracks crossed the Arch: one (the “main way”) to take coal to the River Tyne, and the other (the “bye way”) for returning the empty wagons. Over 900 horse-drawn wagons crossed the arch each day using the Tanfield Railway.
When the bridge was completed in 1726, it was the longest single-span bridge in the country with an arch span of 31 metres (102 ft), a record it held for thirty years until 1756 when the Old Bridge was built in Pontypridd, Wales. After he designed the bridge, Ralph Wood was so afraid that his arch would collapse that he committed suicide, but the bridge still stands today (Wikipedia)